In the spring of 1945, with the largest war in history still being fought across two oceans, the United States War Department stopped to publish a book about how to take a watch apart, clean it, oil it, and put it back together. That fact alone tells you how the military thought about timepieces. A watch was not jewelry. It was equipment, and equipment gets a manual.
The Document
TM 9-1575 was issued on 6 April 1945, by order of the Secretary of War, under the signatures of General George C. Marshall and Major General J. A. Ulio. Its title is plain: Ordnance Maintenance, Wrist Watches, Pocket Watches, Stop Watches, and Clocks. Inside is exactly what the cover promises, a depot-level technical manual for the people responsible for keeping military time running.
It covers the watches a soldier actually carried. The Hamilton 987A on the wrist. The railroad-grade Hamilton 992B in the pocket, a 21-jewel movement built to the same standard that once kept trains from hitting each other. Elgin and Waltham field watches in several jewel counts. The Bulova waterproof. The Elgin stop watches used to time everything from an artillery mission to a foot patrol. And the eight-day Message Center Clock M1. For each, the manual lays out inspection, disassembly, cleaning, oiling, regulating, troubleshooting, and reassembly, down to the warning that a single shock can bend a pivot or chip a jewel and put the whole instrument out of service.
Time as Ordnance
The word that matters is in the title. Ordnance. The same branch that maintained the rifles, the artillery, and the ammunition also maintained the watches, in the same system, by the same kind of trained technician. The Army did not file timepieces under comfort items. It filed them under things that win or lose engagements.
Because timing was a weapon. Artillery arrives on target because everyone agreed on the second. Paratroopers leave the aircraft on a count. Patrols move and return inside windows measured in minutes. Navigation at sea and in the air is a math problem with time on one side of it. A watch that drifted or died was not an inconvenience, it was a mission risk, so the Army treated accuracy as something to be maintained on a schedule: cleaned, oiled, and regulated, by the book, by a technician with the right tools and TM 9-1575 open on the bench.
Why We Carry the Number
This page is about the watches worn in service, the tools that were present for the work. TM 9-1575 is the proof that the idea is neither ours nor new. The military wrote it down in 1945: a watch is a serviceable instrument, cared for like ordnance, because the time it keeps is part of the fight.
So this section borrows the designation and carries it forward. Everything that follows, TM 9-1575-0001 and on, is a manual in that lineage. The watch, the wearer, the work, documented the way the Army documented its own. Tempus Est Potentia is not a slogan we invented. It is the principle the War Department acted on with a wrench and an oiler more than eighty years ago. Time is power, and power gets maintained.
The original is in the public domain and worth an afternoon. You can read TM 9-1575 in full at the Internet Archive.