"Sterile" Issue
Manufactured by the Benrus
Watch Co, Type I watches
were issued to CIA, Navy
Seals and other Special
Forces units during the
Vietnam war and through the
late 70s. The "sterile" issue
differs from the more
common Types I and II
watches by the fact that it has
no military issue engravings
on the case  back. Other than
the serial number, no other
markings can be seen on the
watch. It is thought by many
that the "sterile" watches
were issued to covert
operators. This lack of
identification on the watch
would maintain a level of
deniability in the event the
soldier was captured during a
covert operation.

Another less exotic (but
probably more believable)
theory regarding these
"sterile" watches is they were
unmarked prototypes issued
for testing prior to regular
production.
Benrus Type I "Sterile"
US Issue

Case Diameter: 43 mm
Case Height: 16 mm
Case length: 47.5 mm
Lug Width: 19.5 mm
Movement: Benrus signed GS1D2,
17 jewel, hacking automatic. This is a
ETA 2620 movement modified (by
Benrus) to meet government
specifications. 21,600 bph, 42 hr.
power reserve.
Case material: Stainless steel,
anti-magnetic to 125 gauss
Crown: screw down
Bezel: Bi-directional, no index
Water resistance: 1,200 feet
Vintage: Early '70s