USS MULLINNIX DD-944

Vietnam 1972 - Page 15

RAP (Rocket-Assisted Projectile)

RAP ammunition was a gun-launched, rocket-assisted projectile used by Mullinnix and other ships in the Vietnam War. Its intent was to extend the maximum range of the 5"/54 gun mounts.


Range of Conventioanal Ammo

Naval gunfire considerations included the following:

• It had a flat trajectory that made it effective against vertical-face targets but ineffective against rear-slope targets
• It can deliver a high volume of fire in a short period of time
• It may provide precision guided munitions
• It has a large range error. Try to avoid firing over or near friendly units. Fire parallel to the forward line of own troops (FLOT)
• It is less accurate in rough seas
• It has limited communications between ship and shore
• The only US NGF weapon system available now is the 5-inch/54 found primarily on destroyers
• It is generally coordinated and executed through the support of liaison personnel organic to the air and naval gunfire liaison company (ANGLICO)


RAP Characteristics

As the tables above show, the range of 5"/54 guns was extended 6,ooo+ yards with RAP projectiles. That was the good news.

The Bad News

The rocket-assisted projectiles (RAP) initially worked as advertised. They extended the range of Mullinnix’s 5”/54 guns by up to 6,000 yards. With the number of missions and the excessive wearing on the gun barrels, the inside diameter slowing but surely increased in size.

The barrels became so worn that you could literally see and hear our shells "waffling" through the air as they left the ship to their targets. As a Fire Control Technician, every 6 hours, we updated our calculations in the main fire control computer for RAP Projectiles. As the shells reached their zenith of trajectory, the rocket engine was programmed to kick in to give us the extra range. When these shells were "waffling", the spotters started reporting our shells were hitting all over the place due to these RAP Projectiles careening off course at the top of their trajectory. Our accuracy became greatly diminished until we re-barreled the gun mounts.

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