Seiko has produced quite a few watches for militaries throughout the world over the years, such as the 7A28-7120 and 7T27-7A20 chronographs.  The 7A28 and its successor, the 7T27, were known as the British Royal Air Force Gen 1 and RAF Gen 2, respectively, because as you may have guessed, both were well-known RAF-issued watches - like the 1986 Seiko 7A28-7120 here, with full military markings on the caseback indicating it was issued to the UK RAF. 
 
Seiko provided the 7A28s to RAF from late 1984 through late 1990, for a total of 11,307 examples.  7A28s came in two variants: one with Promethium-147 lume (signified by an encircled “P” on the dial; Promethium being a mildly radioactive emitter), issued to the RAF, and another version without luminous markings, which was issued to the British Royal Navy, primarily for crew on HM nuclear submarines.  Presumably, the lack of luminescent meant it could also be used in any environment where luminous material might interfere with sensitive military equipment.
 
Per Worn&Wound, "In the early 1980s, the military forces of the UK went looking for a new pilot chronograph to replace the Valjoux 7733-powered chronographs they had been issuing for the previous decade.  By this time, quartz technology had advanced to a level of quality and affordability that made it the obvious choice for the new watch."
 
"The company selected to manufacture the new watch was the Japanese company Seiko, marking a departure from the Swiss, American, and English brands the Ministry of Defence had previously used.  It’s no surprise that the MoD decided to look east for their new watch.  Seiko had been producing excellent quartz watches for years, and the watch they provided was a fantastic example of everything a quartz chronograph could be..."
 
By 1990, Seiko ended both the 7A28 and 7T27 (the earlier luminescent version) calibers in favor of the 7T32 alarm chronograph – Seiko went on to produce military-looking 7T32s subsequent, but none were military-issued timepieces.   However, in 1993, Seiko did supply the Royal Navy for sub crews from 1993 through 2000, in quite small numbers.
 
In 1983, Seiko unveiled to the world the first ever quartz analog chronograph, the 7A28 - a 15 jewel, fully adjustable quartz movement with zero plastic parts in the gear train and a movement that can be serviced and adjusted just like a mechanical watch due to its innovative construction.
 
With it, Seiko and its 7A28 entered history as the world’s first analog quartz movement - the Japanese company would release the 7A28 in many notable watches, which would grow to eventually number over forty variations, including models issued to the military and those used in movies (including James Bond and Aliens, among others); some were issued to UK military forces and others to the South African Air Force. 
 
Again, per Worn&Wound, “Prior to its introduction in the early 1980s, all previous chronographs had either been analog (with hands) powered by a mechanical, spring-powered movement, or digital (with a screen) powered by a quartz movement.  The 7A28 paved the way for the affordable, reliable, and stylish quartz analog chronographs we see on the market today.  The use of metal gears throughout the movement made it robust and easily repaired, meaning the watches can last a very long time if well maintained.”
 
Unlike with the above Seiko Ref. 6139, the company sought to publicize this first, advertising the 7A28 series as “Watch History Being Made.”  Seiko would market the 7A28’s to high-end customers, often featuring a number of 7A28 variants propped against the dashboards of luxury vehicles such as the Porsche 911 and Audi Quattros.  Multiple 7A28 variants were even featured in the 1986 sci-fi flick “Aliens,” with another used in the James Bond film “A View to a Kill,” starring Roger Moore.
 
This Seiko 7A28 quartz watch comes with two nylon straps (like on many military-issue watches, springbars are afixed and non-removable), springbar tool, and hard plastic travel case.