International Standardization Agreements. NATO Allied Ordnance Publication (AOP) -20 is the subject of an international Standardization Agreement. NATO Standardization Agreement (STANAG) 4 157@ Fuzing Systems: Test Requirements for Assessment of Safey and Suitability for Service is the implementing document for AOP-20. AOP-20 is derived from US Military Standard 331. Table I presents a cross reference between those tests required in STANAG 4157@ and the test methods presented in this document. Where applicable@ information relating to NATO usage of the test procedures included in this document is presented in Section 7 of the specific test. Application. This standard generally applies to all fuzes@ as well as components of weapon systems serving a fuze function@ such as torpedo exploders and underwater mine firing mechanisms. Test identification. The detailed requirements are documented as individual tests and contained as appendices to this standard. Each test is identified by an alpha-numeric sequence which begins with a letter indicating the test group. This is followed by a sequentially-assigned number. Method of revision. Tests are revised on an individual basis and issued as change notices when required. Revised tests are identified by a decimal number after the test number. Revised test parameters affecting test results apply to fuzes developed subsequent to the change notice. All current test requirements are described in the first five sections of the test. Superseded test requirements with applicable dates are located in Section 6 of the test and identified as alternate tests for older fuzes. Method of reference. Specific tests or test sequences may be invoked by the developing or procuring agency within a formal engineering development test plan or procurement specification. Additionally@ many tests permit variations which should be selected at the time the test is invoked. Variations may include test configuration@ materials@ methods@ sample size or pass fail criteria. Decimal number revisions shall not be referenced.