US Government Specification Field Watch

Read the whole caseback, not just the specification line

A genuine issued caseback carries the specification, a stock or part number, a contract number and a date, stamped rather than laser-etched, with the shallow and slightly uneven depth of period tooling. Reproduction casebacks exist and are usually too clean: uniform character depth, a modern typeface, and often a plausible-looking contract number that does not correspond to a real contract period. The date and the contract must agree with each other and with the specification's own production window.

A correct caseback on the wrong watch is the common problem

Because the caseback carries the valuable part of the identity and it unscrews, the frequent construction is a genuine issued caseback fitted to a civilian case, or a genuine case rebuilt with a replacement dial and hands. Judge the watch as a system: case finish, dial printing, hand style, movement and caseback all have to belong to the same contract period. Any one of them in isolation proves very little.

Radioactive-material marking is period evidence

Tritium-lumed military dials carry the marking required at the time, with the radiation symbol in the position specified for that contract. Its presence, form and position are period-specific and are not usually reproduced correctly on a replacement dial. Note also that tritium lume from this era is long dead: a military dial of the period that glows brightly has been relumed.