On January 15, 1947 the U.S. Navy released a new divers wristwatch Military Specification: 18W8 (SHIPS) / WATCHES, WRIST (WATERTIGHT), which superseded the 18W8 (INT) specification from December 1, 1944. Elgin was the sole manufacturer of watches meeting this new specification, but didn't do so for several years after its release. Primarily issued in the early 1950s to U.S. Navy Underwater Demolition teams, when the teams were conducting vital experimentation with new equipment such as underwater breathing apparatus, wet and dry suits, and developing new delivery methods aboard submarines, such as the USS Perch.
"US Navy frogmen bobbing up in the water off the Virgin Islands." ... mid-1955.
The specification called for a metal dial, finished in a durable, lusterless black and be graduated to minutes. Each fifth minute is indicated by a dot approximately 1/32 inch in diameter, except figure 12, which displays two dots of like material and size directly above the figure 12. Each tenth minute is marked in plain, arabic figures, except for the 60, which is indicated by the 2 dots, one above the other. The dial is also marked ELGIN / USN BUSHIPS in glossy black (difficult to read and photograph due to the black on black printing). The minute and hour hands are of the skeleton type and filled with luminous radioactive material; the second hand is a sweep type and white, except for 3/16 of the tip end, which is treated with luminous material.
Unlike its predecessor, the case and screw down casebacks of each watch were required to be made of stainless steel. To insure the watch remain watertight the case is constructed with a screw cap "on the pipe" which encloses the crown and winding arbor. The screw cap is provided with a Koroseal gasket to insure a water tight seal around the crown and winding arbor when the cap is screwed into place. The cap is attatched to the case by flexible links and a second Koroseal gasket is found in back of the case, to form a watertight joint when the caseback is screwed into place.
The specification required the following test to determine the watches' watertight capabilities:
"F-2b. Watertight test. - Each of the 5 watches selected as specified in paragraph -2a(3) shall be suspended in a beaker of water placed in a vacuum chamber evacuated to 3.5 inches of mercury for a period of 3 minutes."
A fellow watch collector (Lex of MWR) has provided the following information in regard to a possible "real-world" answer to the test above:
3.5in of mercury is approximately 0.1ATM - Assuming that seals work as well for positive or negative pressure:
Since the test is verifying that the seals can withstand a pressure differential of about 10x (1ATM inside the watch vs 0.1ATM outside), we can make a conclusion that the watch would also be able to withstand being immersed to 10 x 1 ATM = 10ATM = 100 meters = 300 ft depth.
The cystal is tempered glass, with a metalized rim, which is soldered to the bezel of the case to insure a watertight seal.
The movement was required to run not less than 30 hours on one winding, be stem-winding and setting, with movements no larger than 6/0 nor smaller than 8/0. In addition the movement was required to have not less than 15 jewels and a daily accuracy rate of -/+ 30 seconds. Elgin produced the watch with the 17 jewel Grade 647 movement, which met all requirements of the new specification.
Two variations of caseback markings are found on the Elgin "Canteen" - either engraved: USN BUSHIPS or USN xxxC (the xxx = unique serial number). Both are correct, and no discernable pattern or trend has been discovered based upon serial numbers of the movments.
Photos of movement, BUSHIPS caseback, and soldered crystal kindly provided by Ian P. of MWR - they remain his property and are used here with permission.
