USS Cassin Young DD-793 - Mark 1a Fire Control Computer  


Dimensions:  62"L x 38"W x 45"H with Star Shell Computer in place over-all height was 65"

Weight:  3125 lbs plus 215lbs for the Star Shell Computer

Cost:  $75,000 ($1,032,875.72- 2014 $)



In the early 1930’s Ford Instrument Co. introduced the Mark 1 Fire Control Computer. About 1935 Ford Instrument Co. added the ability to the Mark 1 computer to compute rate changes in elevation or the z coordinate.

The Mark 1 could compute in elevation, it just could not compute rate changes in terms of elevation.  It knew if the target was on top of a mountain, but that was about all it could do in elevation calculations.  It could not tell if the target was moving in elevation.  The ballistics cut for the Mark 1 were only for surface-to-surface firing and there were no provisions for the surface-to-air calculations needed for the anti-aircraft role.

The Mark 1A overcame this little problem. It also changed the maximum allowed target speed of about 200 knots up to about 450 knots.

The new computer design became the Navy’s first Dual-Purpose computer, as it could handle aircraft targets as well as surface targets. When coupled to the 5”/38 gun, the Navy now had the finest anti-aircraft fire control system in the world.  No other Navy could match this FC system throughout World-War II.  The British purchased this system for use on their ships, but only a single anti-aircraft cruiser actually saw service with it during the war.

The Mark 1A dual purpose computer together with the 5”/38 in single and twin mounts were deployed on almost every USN ship from destroyers through battleships and carriers by the end of the war.

The Mark 1A is what made the 5"/38 the most successful dual-purpose gun of the war as it gave those guns true anti-aircraft capability.  No other nation came close to developing the computer-gun combination so well.

As the Jet-age came about in the late 40’s, the computer was modified to allow maximum target speed about 650 knots.  Our jets were approaching the breakneck speed of 550 knots.  There were many who thought that the sound barrier would not be broken.

As far as I know the only ballistics that were ever cut and installed in the Mark 1A were for the 5”/38 gun until just about wars end.  At that time, the 5”/54 was being introduced on the USS Midway class carriers.  This weapon had different ballistic characteristics and needed different computations than did the 5"/38.