MIL-HDBK-765, MILITARY HANDBOOK: GUIDELINES FOR SAFE DESIGN OF POLYPHASE ELECTRICAL SYSTEMS (14 JUL 1988) [NO S/S DOCUMENT]., Covered in this handbook are polyphase electrical systems used by the US Army that either may be powered continuously by an engine-driven-generator set or powered by a backup engine-driven-generator set, which supplies power when the primary supply is disabled.