Exhibit 10a -  Signet Bank letter, dated May 13, 1994, 
                    re: Credit Facilities to AAI - Page 12


                             [Letterhead of SIGNET BANK]


                                             May 13, 1994

          BY HAND DELIVERY

          Mr. Richard R. Erkeneff
          President
          AAI Corporation
          P. O. Box 126
          Hunt Valley, Maryland  21030

                  Re: Signet Bank/Maryland Credit Facilities to AAI

          Dear Mr. Erkeneff:

               By letter to Paul Michaud dated April 4, 1994, the
          undersigned memorialized previous conversations held with Mr.
          Michaud pursuant to which AAI was advised that the availability
          of additional credit under our Amended and Restated Loan
          Agreement dated as of August 11, 1992, as amended (the "Loan
          Agreement") would terminate on April 30, 1994, and that all
          outstanding "Obligations" (as defined in the Loan Agreement)
          would be due and payable on such date.  As of April 30, the
          obligations of AAI to Signet Bank had not been satisfied, and AAI
          has requested Signet Bank to continue extending credit under the
          Loan Agreement in order to provide sufficient additional time to
          arrange for replacement financing.

               The purpose of this letter is to advise you of the terms
          under which Signet Bank is willing to extend additional credit to
          AAI under the Loan Agreement.  Capitalized terms used in this
          letter without definition which are defined in the Loan Agreement
          shall have the same meanings assigned to such terms in the Loan
          Agreement.

               The Lender hereby consents to an extension of the
          Termination Date to August 20, 1994 (the "Termination Date"),
          upon the following terms and conditions:

               1.   From and after the date hereof, the Maximum Loan Amount
          shall be $7,500,000.00 minus the face amount of all issued and
          outstanding Letters of Credit; provided, however, that for
          purposes of determining whether the Maximum Loan Amount has been
          exceeded, Letter of Credit S1881 and Letter of Credit S1764 (the
          "Excluded Letters of Credit") shall be excluded.

               2.   From and after the date hereof, the Maximum Letter of
          Credit Facility Amount shall be equal to the amount available to
          be drawn as of the date of this letter under the currently
          outstanding Letters of Credit (other than the Excluded Letters of
          Credit).



               3.   On or before May 20, 1994, pursuant to written
          agreements in form and substance satisfactory to the Lender (a)
          the Borrower shall grant to the Lender a first priority security
          interest in all accounts receivable of the Borrower, and (b) UIC
          shall grant to the Lender a first priority security interest in a
          certain note receivable with a current outstanding principal
          balance of $8,540,000.00 which is further described in footnote 4
          to the consolidated financial statements of UIC in the 1993
          Annual Report of UIC, together with all rights of UIC under any
          and all letters of credit and other collateral securing the
          repayment thereof.  The foregoing security interests to be
          granted to the Lender shall be subject only to the rights of
          Principal Mutual Life Insurance Company, The Travelers Insurance
          Company and The Travelers Indemnity Company of Rhode Island
          (collectively, the "Creditor") under the Inter-Creditor Agreement
          dated August 11, 1992, by and among the Lender, the Creditor, the
          Borrower and UIC.  The Borrower and UIC shall execute and deliver
          to the Lender upon the Lender's demand such security agreements,
          financing statements and other documents and instruments as the
          Lender may reasonably require in order to establish and perfect
          the aforementioned security interest.

               4.   The Borrower shall pay to the Lender, concurrently with
          its acceptance hereof, an extension fee in the amount of
          $75,000.00 (the "Extension Fee"); provided, however, that the
          Borrower shall be entitled to a rebate of such Fee in the event
          that all outstanding obligations are satisfied more than thirty
          days prior to the Termination Date.  The amount rebated to the
          Borrower shall equal (a) $50,000.00 if the Obligations are
          satisfied more than sixty days prior to the Termination Date, and
          (b) $25,000.00 if the Obligations are satisfied more than thirty
          (but less than sixty-one) days prior to the Termination Date. 
          The Obligations of the Borrower with respect to outstanding
          Letters of Credit shall not be deemed satisfied unless (i)
          replacement letters of credit have been issued by another
          institution with the result that the Letters of Credit shall have
          been terminated and all of the Lender's obligations thereunder
          discharged, or (ii) the Lender shall have been provided, pursuant
          to a written agreement or agreements satisfactory to the Lender
          and with the concurrence of the Creditor, cash collateral for
          such obligations in an amount not less than the maximum potential
          reimbursement an other obligations of the Borrower in connection
          with such Letter of Credit.

               5.   Each Letter of Credit currently outstanding or issued
          after the Borrower's acceptance hereof shall be subject to the
          requirement that if it is to extend beyond the Termination Date,
          on or before such Termination Date the Borrower shall (a) have
          arranged for the issuance of a replacement letter of credit by
          another institution with the result that such Letter of Credit
          shall be terminated and all of the Lender's obligations
          thereunder discharged, or (b) have provided, pursuant to a
          written agreement or agreements satisfactory to the Lender and
          with the concurrence of the Creditor, cash collateral in form and
          substance satisfactory to the Lender in an amount not less than
          the maximum potential reimbursement and other obligations of the
          Borrower in connection with such Letter of Credit.  The
          requirements of this Paragraph 5 are consistent with the terms
          and conditions of our letter agreement dated August 2, 1993.


               6.   The Borrower shall pay on the demand of the Lender all
          expenses paid or incurred by the Lender (including the fees and
          expenses of its counsel) in connection with (a) the preparation
          and negotiation of this letter agreement and all other documents
          and agreements referred to herein, and (b) all future matters
          arising in connection with the Lender's credit extensions to the
          Borrower.

               Until the terms under which the Lender is willing to extend
          credit to the Borrower have been agreed upon, no additional
          credit will be extended to the Borrower.  The offer contained in
          this letter shall expire on May 16, 1994 unless previously
          accepted by the Borrower and UIC.  Acceptance shall be indicated
          by the Borrower and UIC signing this letter in the space provided
          below, and returning this letter, together with payment of the
          Extension Fee, to the Lender.  An additional copy of this letter
          is also enclosed for your records.

               In the event the Borrower does not find the proposed terms
          of extension as described above to be acceptable, the Borrower
          should arrange for the satisfaction of the outstanding
          Obligations (including, without limitation, the satisfaction of
          the outstanding Letters of Credit on the terms outlined in this
          letter) on or before May 16, 1994.

               Please call (332-5144) if you should have any further
          questions or comments concerning this matter.

                                             Yours truly,

                                             /S/ David A. Bauereis

                                             David A. Bauereis
                                             Vice President

          96/nea

          Enclosure

          cc:  Mr. Paul J. Michaud
               Kevin G. Gralley, Esquire

          ACCEPTED AND AGREED THIS ____
          DAY OF MAY, 1994

          AAI CORPORATION
          AAI ENGINEERING SUPPORT, INC.
          AAI MANUFACTURING ASSEMBLY, INC.
          AAI SYSTEMS MANAGEMENT, IN.
          AAI MEDICAL CORPORATION
          SETI, INC.
          AAI/ACL TECHNOLOGIES, INC.
          AAI MICROFLITE SIMULATION INTERNATIONAL CORPORATION

          By:     /s/ Richard Ray Erkeneff
             Name: RICHARD RAY ERKENEFF
             Title:President & CEO AAI 

          UNITED INDUSTRIAL CORPORATION

          By:   /s/ Howard M. Bloch       
              Name: HOWARD M. BLOCH  
              Title:Vice President -Treasurer