Naval 3-Inch Mark 21 Mount

Left and right-side views of the Mark 21 mount for the 3-inch/50 cal. naval gun from Naval Ordnance and Gunnery, NAVPERS 16116, Bureau of Naval Personnel, Training Division, May 1944.

The 3-inch/50 cal. gun and mount (Mark 21); left-side view.

The 3-inch/50 cal. gun and mount (Mark 21); right-side view.

The 3-inch/50 cal. gun and mount (Mark 21); left-side view.

The 3-inch/50 cal. gun and mount (Mark 21); left-side view.


Length of Bursts for B-29 Gunners

Recommended length of machine gun length for B-29 gunners. Source: Combat Crew Manual, XX Bomber Command, December 1944.


There are several factors to consider in arriving at an answer to the question of how long a burst it is practical to fire. The ammunition has a high degree of accuracy. At 600 yards, when fired from an accuracy rifle held in a V-block, it will group in a circle 18″ in diameter. When fired single shot, using an aircraft machine gun on a tripod mount, tests have shown a 20″ circle of fire. In a burst of 10 or 12 on the same mount the group was approximately five feet. When longer bursts were fired, it was observed that the gun soon lost accuracy, even though it remained relatively stationary in the mount. When over fifty rounds were fired, in one burst, the projectiles tumbled in flight and dispersed over a 75 foot area at 600 yards. When the barrel has been overheated, it will be found that it cannot be relied upon for further accuracy even though the lands and grooves measure up well and the barrel, to all appearances, seems good. If the exterior of the barrel has a burned appearance, it should be tested by ordnance before further use. When a barrel becomes over-heated it expands to such an extent that the muzzle velocity decreases several hundred feet per second. This decrease continues as the barrel continues to expand, until a point is reached where tumbling of the projectiles takes place and controlled fire is reduced to a few hundred feet. The accuracy of the fire delivered, therefore, depends not only on how steadily the gun is held, but also on the length of the burst, and the condition of the barrel. If a gunner fires short bursts of three to five rounds, constantly using his sights, he will have a tight group and a high degree of accuracy. This is the most effective method of firing your machine guns.


A-26 Invader Gunnery

Instructions on pilot gunnery in the Douglas A-26 Invader from Pilot Training Manual for the A-26 Invader, Headquarters, AAF, Office of Flying Safety.

Douglas A-26 Invader Gunnery

No other plane in the Army packs the forward firepower of the A-26. It is designed, among other uses, for low-level attack and strafing. You must know the location of all your gun switches, how to load your guns, and the principle of air-to-ground gunnery.

All the guns must be loaded and charged while on the ground. Under most circumstances, you don’t have to do this yourself, but the time may come when knowing how to load your gun will save your life. See your armament officer for this information.

When you charge your guns, be certain that the airplane is pointed where there is absolutely no danger of hitting anything or anyone in case of an accidental firing (preferably a gun abutment).

Continue reading A-26 Invader Gunnery

P-61 Black Widow Guns

Northrop P-61 Black Widow Gunnery Equipment from P-61 Pilot’s Flight Operating Instructions:

P-61 Black Widow Guns and Gunnery Equipment

B-29 Remote Control Turret System

Another entry from the Bombardiers’ Information File, War Department, March 1945:


The 4 turrets and tail mount of the B-29 all operate by remote control. The gunners sit at sighting stations inside the fuselage and manipulate their gunsights. Computers, connected to the sights, automatically figure deflections for any fighter within range.

B-29 Superfortress Remote Gun Turrets

A system of control transfer enables gunners to take over control of more than one turret for a single gunsight. For every turret there is a gunner who has first call. The nose gunner is given first call on the upper and lower forward turrets. This affords him the greatest possible fire power with which to meet a frontal attack.

If he doesn’t need the lower turret, he can let one of the side gunners take it over. For instance, he might be using the upper turret to shoot at an enemy coming in high, while at the same time another hostile plane may be coming in low. In such a case, he would give one of the side gunners control of the lower forward turret. Similarly, he can release control of the upper forward turret to the top gunner.

In the nose sighting station there are 3 units of gunnery equipment that are of concern to you, the bombardier:

1. Control box with the necessary switches for operating the turrets and gunsight.

2. Gunsight and controlling equipment.

3. Transfer switches.

An auxiliary switch on the control box starts the compressor motors that operate the gun chargers. A computer standby switch turned to the IN position cuts the computing mechanism into the forward turret circuits.

B-29 Superfortress Bombardier Gunsight for Remote-Control Turrets

To operate both forward turrets, turn both transfer switches to IN and press down on the action switch. The guns in both turrets then follow your gunsight and fire when you press the trigger.

To give up control of one turret, use the transfer switches. When the upper forward turret switch is OUT, the top gunner has control of the upper turret. When the lower forward turret switch is OUT, one of the side gunners takes over the lower turret.

If you take your hand off the action switch, control of both turrets passes automatically to top and side gunners regardless of transfer switch settings.

Warning — Always sound a warning over the interphone before you give up control of either or both turrets. If you don’t, the gunner who takes over may have his finger on the trigger and the guns will spray bullets into your own formation as they swing into line with his sight.

It is your duty to stow the lower forward turret when it is not in use. Run the turret around so that the guns point aft; then turn off the designated switches. The guns will automatically stow at the correct elevation.

A friction adjustment gives the gun sight just the right touch. You will find there is only one right setting for you. Set the sight so that you can track smoothly. Once you have started tracking, don’t change your grip on the hand wheels. Don’t jerk your point of aim. Move it smoothly and don’t fire until you’re on the target.

Cool the guns at every opportunity. If you fire as much as 50 rounds within a short period, look for a chance to move the guns into the slipstream of the airplane—and hold them there.


Bombardier Chin and Nose Turrets

From Bombardiers’ Information File, War Department, March 1945:

B-17 Chin Turret and B-24 Nose Turret - Bombardier Turrets

The bombardier is concerned primarily with those gun turrets he is most likely to operate. He is almost always responsible for control of the nose turrets in heavy and very heavy aircraft.


The chin turret of the B-17 operates electrically by remote control from the bombardier’s seat directly above it. It moves 86° to either side in azimuth, 26° above and 46° below horizontal in elevation. It uses the N-8 or N-6A optical gunsight. The bombardier’s seat remains stationary; as he turns the gunsight, the guns swing around beneath. The bombardier’s control unit, housing the gunsight, pivots out from its stowed position on his right and locks in place in front of him.


The nose turret of the B-24 is an all-electric turret which uses the N-8 or N-6A optical gunsight. It moves in azimuth about 75° either side of the airplane’s center line, and in elevation from 50° below horizontal to 60° above. It has 2 speeds, normal tracking and high. It contains armor plate, and bulletproof glass plate which moves with the guns.


Tank Gun Trajectories

The U.S. WWII field manual FM 17-12: Tank Gunnery illustrated representative trajectories of the 37-mm, 75-mm, and 76-mm guns. Low velocity guns with more highly curved trajectories require very accurate range estimation. As shown in the figures below, even small errors in range estimation reduce the effectiveness of the opening shot and increase the number of rounds required to achieve a hit.

Trajectory 37-mm Gun

Original Caption: Trajectory 37-mm, M6, firing APC, M51B1. This is illustrative only. The 37-mm should not be fired at tanks at ranges shown.

Trajectory 75-mm Gun

Original Caption: Trajectory 75-mm gun, M3, firing shot, APC, M61.

76-mm Gun Trajectory

Original Caption: Trajectory 76-mm gun, M1, firing shot, APC, M62.