EXECUTION COPY
                                     
                         THIRD AMENDMENT dated as of June 29, 1998,
                         to the Credit Agreement dated as of 
                         September 23, 1990 (as amended and restated as
                         of February 7, 1997), as amended by the
                         Amendments dated as of May 6, 1997, and 
                         November 21, 1997 (the "Credit Agreement"),
                         among ESCO ELECTRONICS CORPORATION, a Missouri
                         corporation ("ESCO"), DEFENSE HOLDING CORP., a
                         Delaware corporation (the "Borrower"), the BANKS
                         party thereto (the "Banks") and ▇▇▇▇▇▇ GUARANTY 
                         TRUST COMPANY OF NEW YORK, as Agent (the
                         "Agent").
     
                   A.  Capitalized terms used and not otherwise defined
     herein shall have the meanings assigned to them in the Credit
     Agreement, as amended hereby.
     
                   ▇.  ▇▇▇▇ and the Borrower have requested that certain
     provisions of the Credit Agreement be amended as set forth herein. 
     The Banks are willing to so amend the Credit Agreement subject to 
     the terms and conditions set forth herein.
     
                   Accordingly, in consideration of the mutual agreements 
     herein contained and other good and valuable consideration, the
     sufficiency and receipt of which are hereby acknowledged, the
     parties hereto hereby agree as follows:
     
     
                   SECTION 1.  Amendments.  (a) Section 1.01 of the Credit
     Agreement is hereby amended to add the following definitions:
     
                   "AMT" means Advanced Membrane Technology, Inc., a
             California corporation.
     
                   "AMT Investment" means the acquisition by a Wholly-
             Owned Consolidated Subsidiary of all of the outstanding
             common stock of AMT in exchange for consideration of
             approximately $15,000,000 (adjusted upward to reflect AMT's
             cash at closing and downward to reflect AMT's debt at
             closing) payable approximately 45% in cash and 55% in shares 
             of common stock of ESCO.
     
                   (b)  Article II of the Credit Agreement is hereby
     amended and restated by adding the following Section 2.17 at the
     end of such Article:
     
             SECTION 2.17.  Conversion.  Effective upon the
             consummation of the AMT Investment, (a) Working Capital
             Borrowings in an aggregate principal amount of $7,000,000
             shall be automatically converted into Term Borrowings and (b)
             the Working Capital Commitments shall be ratably reduced by
             $7,000,000.  Prior to the date of such conversion, the
             Borrower shall notify the Agent in writing of the Working
             Capital Borrowing or Borrowings (or portions thereof) that
             are to be converted pursuant to the preceding sentence.  The 
             conversion of each such Borrowing (or portion thereof) shall 
             be allocated ratably to the Loans included in such Borrowing. 
             If the aggregate principal amount of outstanding Working
             Capital Loans would be less than $7,000,000 on the date that
             such conversion is to be made pursuant to the first sentence
             of this Section, then the Borrower shall borrow additional
             Working Capital Loans so that there are not less than
             $7,000,000 in aggregate principal amount of Working Capital
             Loans outstanding at the time of such conversion. 
             Notwithstanding the foregoing, no such conversion shall
             become effective until receipt by the Security Agent of an
             amendment to each mortgage, deed of trust, assignment of
             leases or similar instrument or document required by law or
             reasonably requested by the Security Agent (all in form and
             substance reasonably satisfactory to the Required Banks) to
             be filed, registered or recorded in order to maintain in
             favor of the Security Agent (or a trustee on its behalf) for
             the benefit of the Banks a valid, legal and perfected first
             priority security interest in or lien on the real property
             (and improvements thereon) owned by the Borrower or any
             Specified Subsidiary and identified on Schedule 3.01(j) to
             the Credit Agreement, in each case duly executed and
             delivered by each mortgagor, grantor or pledgor thereunder.
     
             (c)  Section 5.09 of the Credit Agreement is hereby
     amended by deleting the words "clause (f), (l) or (n)" from the
     second sentence thereof and substituting the words "clause (f),
     (l), (n) or (o)".
     
             (d) Section 5.11(a) of the Credit Agreement is hereby
     amended by replacing the period at the end of clause (xiv) thereof 
     with a semicolon and by adding the following clauses (xv) and (xvi)
     at the end of such Section:
     
             (xv) Debt of any Subsidiary acquired pursuant to an
             acquisition consummated in reliance upon clause (f) or (o) of
             Section 5.16; provided that (A) such Debt is outstanding at
             the time of and is not incurred in contemplation of such
             acquisition and (B) the aggregate principal amount of Debt at
             any time outstanding under this clause (xv) shall not exceed
             $1,000,000; and
     
             (xvi) Debt incurred by DCS to finance the purchase of
             real property and improvements thereon to be used by DCS as
             its headquarters, and any Guarantee of such Debt by ESCO;
             provided that the aggregate principal amount of such Debt of 
             DCS at any time outstanding under this clause (xvi) shall not
             exceed $2,500,000.
     
             (e)  Section 5.16 of the Credit Agreement is hereby
     amended by replacing the period at the end of clause (n) thereof
     with "; and" and adding the following clause (o) at the end of such
     Section:  
     
             (o) if at the time thereof and after giving effect
             thereto no Default shall have occurred and be continuing, an 
             Investment by a Wholly-Owned Consolidated Subsidiary
             consisting of the AMT Investment; provided that the cash
             portion of the consideration for such Investment made
             pursuant to this clause (o) and any Debt of AMT remaining
             outstanding after the AMT Acquisition shall be treated as an 
             Investment made pursuant to clause (f) of this Section for
             purposes of determining compliance with the limitations of
             such clause (f).
     
             (f)  Section 5.17 of the Credit Agreement is hereby
     amended by replacing the period at the end of clause (n) thereof
     with "; and" and adding the following clause (o) at the end of such
     Section:
     
             (o) Liens on the real property and improvements referred
             to in clause (xvi) of Section 5.11(a) securing Debt of DCS
             permitted by such clause.
     
             (g)  Section 5.23 of the Credit Agreement is hereby
     amended and restated as follows:
     
             SECTION 5.23.  Leverage Ratio.  The Leverage
             Ratio will not exceed (i) 0.70 to 1.00 at any date prior to
             October 1, 1999, or (ii) 0.65 to 1.00 at any date on or after
             October 1, 1999.
     
             SECTION 2.  Representations and Warranties.  Each of
     ESCO and the Borrower hereby represents and warrants to each Bank, 
     on and as of the date hereof, that:
     
             (a)  This Third Amendment has been duly authorized,
     executed and delivered by each of ESCO and the Borrower, and each
     of this Third Amendment and the Credit Agreement as amended by this
     Third Amendment constitutes a legal, valid and binding obligation
     of each of ESCO and the Borrower, enforceable in accordance with
     its terms.
     
             (b)  The representations and warranties of ESCO, the
     Borrower and its Subsidiaries contained in the Credit Agreement and
     in each other Loan Document are true and correct in all respects
     with the same effect as if made on and as of the date hereof,
     except to the extent that such representations and warranties
     expressly relate to an earlier date.
     
             (c)  After giving effect to this Third Amendment, no
     Default has occurred and is continuing.
     
             SECTION 3.  Effectiveness.  This Third Amendment shall 
     become effective upon receipt by the Agent of counterparts hereof
     signed by each of ESCO, the Borrower and each Bank.
     
             SECTION 4.  Miscellaneous.  (a)  This Third Amendment
     constitutes the entire agreement and understanding of the parties
     with respect to the subject matter hereof and supersedes any and
     all prior agreements and understandings, oral or written, relating 
     to the subject matter hereof.
     
             (b)  Section headings used herein are for convenience
     of reference only and are not to affect the construction of, or to 
     be taken into consideration in interpreting, this Third Amendment.
     
             (c)  This Third Amendment shall be construed in
     accordance with and governed by the law of the State of New York.
     
             (d)  Each reference to a party hereto shall be deemed
     to include its successors and assigns, all of whom shall be bound
     by this Third Amendment and to whose benefit the provisions of this
     Third Amendment shall inure.
     
             (e)  This Third Amendment may be executed in any number
     of counterparts, each of which shall be an original but all of
     which, when taken together, shall constitute but one instrument.
     
             (f)  Except as specifically amended or modified hereby,
     the Credit Agreement shall continue in full force and effect in
     accordance with the provisions thereof.
     
     
             IN WITNESS WHEREOF, the parties hereto have caused this
     Third Amendment to be duly executed by their respective authorized
     officers as of the date first above written.
     
     
                                        ESCO ELECTRONICS CORPORATION 
                     
                     
                                        DEFENSE HOLDING CORP.
                     
                     
                                        ▇▇▇▇▇▇ GUARANTY TRUST COMPANY OF NEW
                                        YORK, individually and as Agent
                     
                     
                                        NATIONSBANK, N.A.
                     
                     
                                        THE BANK OF NEW YORK
                     
                     
                                        THE BANK OF NOVA SCOTIA
                     
                     
                                        NATIONAL CITY BANK
                     
                     
                                        FIRST UNION NATIONAL BANK OF
                                        NORTH CAROLINA
                     
                     
                                        SANWA BUSINESS CREDIT CORPORATION