SIMPSON THACHER & BARTLETT
                              425 LEXINGTON AVENUE
                           NEW YORK, N.Y. 10017-3954
                                 (212) 455-2000

                                    -------

                           FACSIMILE: (212) 455-2502

DIRECT DIAL NUMBER                                                E-MAIL ADDRESS



                                                 March 22, 2002



L-3 Communications Holdings, Inc.
600 Third Avenue
New York, New York 10016

L-3 Communications Corporation
600 Third Avenue
New York, New York 10016

Ladies and Gentlemen:

                    We have acted as counsel to L-3 Communications Holdings,
Inc., a Delaware corporation ("L-3 Holdings"), L-3 Communications Corporation, a
wholly-owned subsidiary of L-3 Holdings and a Delaware corporation ("L-3
Communications"), the Delaware subsidiaries of L-3 Holdings named on Schedule I
attached hereto (each, a "Delaware Guarantor" and collectively, the "Delaware
Guarantors"), the non-Delaware subsidiaries of L-3 Holdings named on Schedule II
attached hereto (each, a "Non-Delaware Guarantor" and collectively, the
"Non-Delaware Guarantors", taken together with the Delaware Guarantors, the
"Subsidiary Guarantors"), in connection with the Registration Statement on Form
S-3 (the "Registration Statement") filed by L-3 Holdings, L-3 Communications and
the Subsidiary Guarantors with the Securities and Exchange Commission (the
"Commission") under the Securities Act of 1933, as amended (the "Act"), relating
to (i) shares of common stock of L-3 Holdings par value $.01 per share (the
"Common Stock"); (ii) shares of Common Stock to be sold by certain selling
stockholders (the "Selling Stockholders"); (iii) shares of preferred stock of
L-3 Holdings par value $.01 per share (the "Preferred Stock"); (iv) warrants to
purchase Common Stock (the "Common Stock Warrants"); (v) warrants to purchase
Preferred Stock (the "Preferred Stock Warrants"); (vi)





SIMPSON THACHER & BARTLETT

   L-3 Communications Holdings, Inc.           2                March 22, 2002
   L-3 Communications Corporation


unsecured debt securities of L-3 Holdings consisting of notes, debentures or
other evidence of indebtedness, which may be either senior ("L-3 Holdings Senior
Debt Securities"), senior subordinated ("L-3 Holdings Senior Subordinated Debt
Securities") or subordinated ("L-3 Holdings Subordinated Debt Securities")
(collectively, the "L-3 Holdings Debt Securities"); (vii) warrants to purchase
L-3 Holdings Debt Securities (the "L-3 Holdings Debt Security Warrants"); (viii)
unsecured debt securities of L-3 Communications consisting of notes, debentures
or other evidence of indebtedness, which may be either senior ("L-3
Communications Senior Debt Securities"), senior subordinated ("L-3
Communications Senior Subordinated Debt Securities") or subordinated ("L-3
Communications Subordinated Debt Securities") (collectively, the "L-3
Communications Debt Securities" and, together with the L-3 Holdings Debt
Securities, the "Debt Securities"), which will be fully and unconditionally
guaranteed by L-3 Holdings (the "L-3 Holdings Debt Guarantee"); (ix) guarantees
of the Subsidiary Guarantors to be issued in connection with the Debt Securities
(the "Debt Guarantees"); (x) contracts for purchase and sale of Common Stock or
Preferred Stock (the "Purchase Contracts"); (xi) Stock Purchase Units of L-3
Holdings, consisting of a Purchase Contract and either a beneficial interest in
L-3 Holdings Debt Securities or debt obligations of third parties, including
U.S. Treasury securities (the "Stock Purchase Units"); and (xii) Common Stock,
Preferred Stock and L-3 Holdings Debt Securities, which may be issued upon
exercise of Securities Warrants (as defined below) or Purchase Contracts,
whichever is applicable. The Common Stock, the Preferred Stock, the Debt
Securities, the L-3 Holdings Debt Guarantee, the Debt Guarantees, the Purchase
Contracts, the Stock Purchase Units and the Securities Warrants are hereinafter
referred to as the "Securities". The Securities may be issued and sold or
delivered from time to time as set forth in the Registration





SIMPSON THACHER & BARTLETT

   L-3 Communications Holdings, Inc.           3                March 22, 2002
   L-3 Communications Corporation


Statement, any amendment thereto, the prospectus contained therein (the
"Prospectus") and supplements to the Prospectus (the "Prospectus Supplements")
and pursuant to Rule 415 under the Act for an aggregate initial offering price
not to exceed ________ or the equivalent thereof in one or more foreign
currencies or composite currencies (together with any additional Securities that
may be issued by L-3 Holdings, L-3 Communications and the Subsidiary Guarantors
pursuant to Rule 462(b) (as prescribed by the Commission pursuant to the Act)).
The Common Stock to be sold by the Selling Stockholders may be sold from time to
time as set forth in the Registration Statement, any amendment thereto, the
Prospectus and the Prospectus Supplements and pursuant to Rule 415 under the Act
in an amount not to exceed [500,000] shares (together with any additional shares
of Common Stock that may be sold by the Selling Stockholders pursuant to Rule
462(b) (as prescribed by the Commission pursuant to the Act)).

                    The L-3 Holdings Debt Securities and the Debt Guarantees
thereof, if applicable, will be issued under an Indenture (the "L-3 Holdings
Indenture") among L-3 Holdings, such Trustee as shall be named therein (the "L-3
Holdings Trustee") and such Subsidiary Guarantors as shall be named therein, if
applicable. The L-3 Communications Debt Securities, the L-3 Holdings Debt
Guarantee and the Debt Guarantees thereof, if applicable, will be issued under
an Indenture (the "L-3 Communications Indenture") among L-3 Communications, L-3
Holdings, such Trustee as shall be named therein (the "L-3 Communications
Trustee") and such Subsidiary Guarantors as shall be named therein, if
applicable. The L-3 Holdings Indenture and the L-3 Communications Indenture are
hereinafter collectively referred to as the "Indentures".

                    The Purchase Contracts will be issued pursuant to a Purchase
Contract Agreement (the "Purchase Contract Agreement") between L-3 Holdings and
a purchase contract agent as





SIMPSON THACHER & BARTLETT

   L-3 Communications Holdings, Inc.           4                March 22, 2002
   L-3 Communications Corporation


shall be named therein (the "Purchase Contract Agent").

                    The Common Stock Warrants, the Preferred Stock Warrants and
the L-3 Holdings Debt Security Warrants are hereinafter referred to collectively
as the "Securities Warrants." The Common Stock Warrants will be issued under a
Common Stock Warrant Agreement (the "Common Stock Warrant Agreement") between
L-3 Holdings and a common stock warrant agent as shall be named therein (the
"Common Stock Warrant Agent"). The Preferred Stock Warrants will be issued under
a Preferred Stock Warrant Agreement (the "Preferred Stock Warrant Agreement")
between L-3 Holdings and a preferred stock warrant agent as shall be named
therein (the "Preferred Stock Warrant Agent"). The L-3 Holdings Debt Security
Warrants will be issued under a Debt Security Warrant Agreement (the "Debt
Security Warrant Agreement") among L-3 Holdings, a debt security warrant agent
as shall be named therein (the "Debt Security Warrant Agent") and the L-3
Holdings Trustee. The Common Stock Warrant Agreement, the Preferred Stock
Warrant Agreement and the Debt Security Warrant Agreement are hereinafter
referred to collectively as the "Warrant Agreements." Each party to a Warrant
Agreement other than L-3 Holdings is referred to hereinafter as a
"Counterparty."

                    We have examined the Registration Statement and the exhibits
filed with the Commission to such Registration Statement on the date hereof. We
also have examined the originals, or duplicates or certified or conformed
copies, of such records, agreements, instruments and other documents and have
made such other and further investigations as we have deemed relevant and
necessary in connection with the opinions expressed herein. As to questions of
fact material to this opinion, we have relied upon certificates of public
officials and of officers and representatives of L-3 Holdings, L-3
Communications and the Subsidiary





SIMPSON THACHER & BARTLETT

   L-3 Communications Holdings, Inc.           5                March  22, 2002
   L-3 Communications Corporation


Guarantors.

                    In rendering the opinions set forth below, we have assumed
the genuineness of all signatures, the legal capacity of natural persons, the
authenticity of all documents submitted to us as originals, the conformity to
original documents of all documents submitted to us as duplicates or certified
or conformed copies, and the authenticity of the originals of such latter
documents. We also have assumed that: (1) at the time of execution,
authentication, issuance and delivery of the Debt Securities, each of the
Indentures will be the valid and legally binding obligation of the trustee
thereunder; (2) at the time of execution, issuance and delivery of the Purchase
Contracts, the Purchase Contract Agreement will be the valid and legally binding
obligation of the Purchase Contract Agent; and (3) at the time of execution,
countersignature, issuance and delivery of any Securities Warrants, the related
Warrant Agreement will be the valid and legally binding obligation of each
Counterparty thereto.

                    We have assumed further that (1) at the time of execution,
authentication, issuance and delivery of the L-3 Holdings Debt Securities, and
the Debt Guarantees, if applicable, the L-3 Holdings Indenture will have been
duly authorized, executed and delivered by L-3 Holdings and the Subsidiary
Guarantors, if applicable and (2) if applicable, execution, delivery and
performance by each Non-Delaware Guarantor of the L-3 Holdings Indenture and the
Debt Guarantees will not violate the laws of its jurisdiction of incorporation
or any other applicable laws (excepting the laws of the State of New York and
the Federal laws of the United States).

                  We have assumed further that (1) at the time of execution,
authentication, issuance and delivery of the L-3 Communications Debt Securities,
the L-3 Holdings Debt





SIMPSON THACHER & BARTLETT

   L-3 Communications Holdings, Inc.           6                March  22, 2002
   L-3 Communications Corporation



Guarantee and the Debt Guarantees, if applicable, the L-3 Communications
Indenture will have been duly authorized, executed and delivered by L-3
Communications, L-3 Holdings, and the Subsidiary Guarantors, if applicable and
(2) if applicable, execution, delivery and performance by each Non-Delaware
Guarantor of the L-3 Communications Indenture will not violate the laws of its
jurisdiction of incorporation or any other applicable laws (excepting the laws
of the State of New York and the Federal laws of the United States).

                    We have assumed further that at the time of execution,
issuance and delivery of the Purchase Contracts, the Purchase Contract Agreement
will have been duly authorized, executed and delivered by L-3 Holdings.

                    We have assumed further that at the time of execution,
countersignature, issuance and delivery of any Securities Warrants, the related
Warrant Agreements will have been duly authorized, executed and delivered by L-3
Holdings.

                    Based upon the foregoing, and subject to the qualifications
and limitations stated herein, we are of the opinion that:


              1.    With respect to the Common Stock, assuming (a) the taking by
                    the Board of Directors of L-3 Holdings, a duly constituted
                    and acting committee of such Board of Directors or duly
                    authorized officers of L-3 Holdings (such Board of
                    Directors, committee or authorized officers being referred
                    to herein as the "L-3 Holdings Board") of all necessary
                    corporate action to authorize and approve the issuance of
                    the Common Stock and (b) due issuance and delivery of the
                    Common Stock, upon payment therefor in accordance with the
                    applicable definitive purchase, underwriting or similar
                    agreement approved by the L-3 Holdings Board, the Common
                    Stock will be validly issued, fully paid and nonassessable.

              2.    With respect to the Common Stock to be sold by the Selling
                    Stockholders, such Common Stock has been duly authorized and
                    is validly issued, fully paid and nonassessable.

              3.    With respect to the Preferred Stock, assuming (a) the taking
                    by the L-3 Holdings Board of all necessary corporate action
                    to authorize and approve the issuance of





SIMPSON THACHER & BARTLETT

   L-3 Communications Holdings, Inc.           7                March  22, 2002
   L-3 Communications Corporation


                    the Preferred Stock, (b) due filing of a Certificate of
                    Designations with the Secretary of State of the State of
                    Delaware and (c) due issuance and delivery of the Preferred
                    Stock, upon payment therefor in accordance with the
                    applicable definitive purchase, underwriting or similar
                    agreement approved by the L-3 Holdings Board, the Preferred
                    Stock will be validly issued, fully paid and nonassessable.

              4.    With respect to the L-3 Holdings Debt Securities, assuming
                    (a) the taking by the L-3 Holdings Board of all necessary
                    corporate action to approve the issuance and terms of any
                    L-3 Holdings Debt Securities, the terms of the offering
                    thereof and related matters and (b) the due execution,
                    authentication, issuance and delivery of such L-3 Holdings
                    Debt Securities, upon payment of the consideration therefor
                    provided for in the applicable definitive purchase,
                    underwriting or similar agreement approved by the L-3
                    Holdings Board and otherwise in accordance with the
                    provisions of the L-3 Holdings Indenture and such agreement,
                    such L-3 Holdings Debt Securities will constitute valid and
                    legally binding obligations of L-3 Holdings enforceable
                    against L-3 Holdings in accordance with their terms.

              5.    With respect to the L-3 Communications Debt Securities,
                    assuming (a) the taking of all necessary corporate action to
                    approve the issuance and terms of any L-3 Communications
                    Debt Securities, the terms of the offering thereof and
                    related matters by the Board of Directors of L-3
                    Communications, a duly constituted and acting committee of
                    such Board of Directors or duly authorized officers of L-3
                    Communications (such Board of Directors, committee or
                    authorized officers being referred to herein as the "L-3
                    Communications Board") and (b) the due execution,
                    authentication, issuance and delivery of such L-3
                    Communications Debt Securities, upon payment of the
                    consideration therefor provided for in the applicable
                    definitive purchase, underwriting or similar agreement
                    approved by the L-3 Communications Board and otherwise in
                    accordance with the provisions of the L-3 Communications
                    Indenture and such agreement, such L-3 Communications Debt
                    Securities will constitute valid and legally binding
                    obligations of L-3 Communications enforceable against L-3
                    Communications in accordance with their terms.

              6.    With respect to the L-3 Holdings Debt Guarantee and the Debt
                    Guarantees (collectively, the "Guarantees"), assuming (a)
                    the taking of all necessary corporate action to approve the
                    issuance and terms of the Guarantees and related matters by
                    the L-3 Holdings Board and by the Board of Directors of each
                    Subsidiary Guarantor (or in the case of a Subsidiary
                    Guarantor that is a partnership, the Board of Directors of
                    the general partner), as applicable, a duly constituted and
                    acting committee of such Board of Directors of a Subsidiary
                    Guarantor or duly authorized officers of a Subsidiary
                    Guarantor (each such Board of Directors, committee or
                    authorized officers being referred to herein as a
                    "Subsidiary Guarantor Resolution"), (b) the due execution,
                    authentication,





SIMPSON THACHER & BARTLETT

   L-3 Communications Holdings, Inc.           8                March  22, 2002
   L-3 Communications Corporation


                    issuance and delivery of the Debt Securities underlying such
                    Guarantees, upon payment of the consideration therefor
                    provided for in the applicable definitive purchase,
                    underwriting or similar agreement approved by the L-3
                    Holdings Board and such Subsidiary Guarantor Resolution, as
                    applicable, and otherwise in accordance with the provisions
                    of the applicable Indenture and such agreement and (c) the
                    due issuance of such Guarantees, such Guarantees will
                    constitute valid and legally binding obligations of L-3
                    Holdings and such Subsidiary Guarantors, as applicable,
                    enforceable against the L-3 Holdings and such Subsidiary
                    Guarantors, as applicable, in accordance with their terms.

              7.    With respect to the Purchase Contracts, assuming (a) the
                    taking of all necessary corporate action by the L-3 Holdings
                    Board to approve the execution and delivery of the Purchase
                    Contract Agreement and (b) the due execution, issuance and
                    delivery of the Purchase Contracts, upon payment of the
                    consideration for such Purchase Contracts provided for in
                    the applicable definitive purchase, underwriting or similar
                    agreement approved by the L-3 Holdings Board and otherwise
                    in accordance with the provisions of the applicable Purchase
                    Contract Agreement and such agreement, the Purchase
                    Contracts will constitute valid and legally binding
                    obligations of L-3 Holdings enforceable against L-3 Holdings
                    in accordance with their terms.

              8.    With respect to the Securities Warrants, assuming (a) the
                    taking of all necessary corporate action by the L-3 Holdings
                    Board to approve the execution and delivery of a related
                    Warrant Agreement and (b) the due execution,
                    countersignature, issuance and delivery of such Securities
                    Warrants, upon payment of the consideration for such
                    Securities Warrants provided for in the applicable
                    definitive purchase, underwriting or similar agreement
                    approved by the L-3 Holdings Board and otherwise in
                    accordance with the provisions of the applicable Warrant
                    Agreement and such agreement, such Securities Warrants will
                    constitute valid and legally binding obligations of the L-3
                    Holdings enforceable against L-3 Holdings in accordance with
                    their terms.

              9.    With respect to the Stock Purchase Units, assuming (a) in
                    the case of Stock Purchase Units consisting at least in part
                    of debt obligations of third parties, such debt obligations
                    at all relevant times constitute the valid and legally
                    binding obligations of the issuers thereof enforceable
                    against the issuers thereof in accordance with their terms,
                    (b) the taking of all necessary corporate action by the L-3
                    Holdings Board to authorize and approve (1) the issuance and
                    terms of the Stock Purchase Units, (2) the execution and
                    delivery of the Purchase Contract Agreement with respect to
                    the Purchase Contracts which are a component of the Stock
                    Purchase Units and (3) in the case of Stock Purchase Units
                    consisting at least in part of L-3 Holdings Debt Securities,
                    the issuance and terms of the L-3 Holdings Debt Securities
                    which are a component of the Stock Purchase Units, the terms
                    of the offering thereof and related matters and (c) the due
                    execution,





SIMPSON THACHER & BARTLETT

   L-3 Communications Holdings, Inc.           9                March  22, 2002
   L-3 Communications Corporation


                    authentication, in the case of such Debt Securities,
                    issuance and delivery of (1) the Stock Purchase Units, (2)
                    such Purchase Contracts and (3) in the case of Stock
                    Purchase Units consisting at least in part of L-3 Holdings
                    Debt Securities, such Debt Securities, in each case upon the
                    payment of the consideration therefor provided for in the
                    applicable definitive purchase, underwriting or similar
                    agreement approved by the L-3 Holdings Board and in
                    accordance with the provisions of the applicable Purchase
                    Contract Agreement, in the case of such Purchase Contracts,
                    and the applicable L-3 Holdings Indenture, in the case of
                    such L-3 Holdings Debt Securities, such Stock Purchase Units
                    will constitute valid and legally binding obligations of L-3
                    Holdings, enforceable against L-3 Holdings in accordance
                    with their terms.

                    Our opinions set forth in paragraphs 4 through 9 above are
subject to the effects of (i) bankruptcy, insolvency, fraudulent conveyance,
reorganization, moratorium and other similar laws relating to or affecting
creditors' rights generally, (ii) general equitable principles (whether
considered in a proceeding in equity or at law), and (iii) an implied covenant
of good faith and fair dealing.

                    We are members of the Bar of the State of New York, and we
do not express any opinion herein concerning any law other than the law of the
State of New York, the Federal law of the United States and the Delaware General
Corporation Law (including the statutory provisions, all applicable provisions
of the Delaware Constitution and required judicial decisions interpreting the
foregoing).

                    We hereby consent to the filing of this opinion letter as
Exhibit 5 to the Registration Statement and to the use of our name under the
caption Legal Matters in the Prospectus included in the Registration Statement.



                                       Very truly yours,


                                       /s/ Simpon Thacher & Bartlett
                                       ---------------------------------------
                                       SIMPSON THACHER & BARTLETT







SIMPSON THACHER & BARTLETT

   L-3 Communications Holdings, Inc.           10                March  22, 2002
   L-3 Communications Corporation


                                   SCHEDULE I

DELAWARE GUARANTORS
- -------------------


HYGIENETICS ENVIRONMENTAL SERVICES, INC., a Delaware Corporation
L-3 COMMUNICATIONS ILEX SYSTEMS, INC., a Delaware Corporation
L-3 COMMUNICATIONS SPD TECHNOLOGIES INC., a Delaware Corporation
L-3 COMMUNICATIONS ESSCO, INC., a Delaware Corporation
SPD ELECTRICAL SYSTEMS, INC., a Delaware Corporation
SPD SWITCHGEAR, INC., a Delaware Corporation
PAC ORD INC., a Delaware Corporation
HENSCHEL INC., a Delaware Corporation
SPD HOLDINGS, INC., a Delaware Corporation
POWER PARAGON, INC., a Delaware Corporation
L-3 COMMUNICATIONS AYDIN CORPORATION, a Delaware Corporation
L-3 COMMUNICATIONS INTEGRATED SYSTEMS L.P., a Delaware Limited Partnership
L-3 COMMUNICATIONS AIS GP CORPORATION, a Delaware Corporation
L-3 COMMUNICATION INVESTMENTS INC., a Delaware Corporation
MPRI, INC., a Delaware Corporation
KDI PRECISION PRODUCTS INC., a Delaware Corporation













SIMPSON THACHER & BARTLETT

   L-3 Communications Holdings, Inc.           11                March  22, 2002
   L-3 Communications Corporation


                                   SCHEDULE II

NON-DELAWARE GUARANTORS
- -----------------------


SOUTHERN CALIFORNIA MICROWAVE, INC., a California Corporation
L-3 COMMUNICATIONS STORM CONTROL SYSTEMS INC., a California Corporation
L-3 COMMUNICATIONS DBS MICROWAVE, INC., a California Corporation
MICRODYNE CORPORATION, a Maryland Corporation
ELECTRODYNAMICS, INC., an Arizona Corporation
INTERSTATE ELECTRONICS CORPORATION, a California Corporation
COLEMAN RESEARCH CORPORATION, a Florida Corporation
EER SYSTEMS, INC., a Virginia Corporation
L-3 COMMUNICATIONS ANALYTICS CORPORATION, a California Corporation
AMI INSTRUMENTS, INC., an Oklahoma Corporation
L-3 COMMUNICATIONS ATLANTIC SCIENCE AND TECHNOLOGY CORPORATION, a New Jersey
    Corporation
MICRODYNE COMMUNICATIONS TECHNOLOGIES INCORPORATED, a Maryland Corporation
APCOM, INC., a Maryland Corporation
CELEBRITY SYSTEMS INCORPORATED, a California Corporation
MICRODYNE OUTSOURCING INCORPORATED, a Maryland Corporation