The Maxon M45 power turret mounted four .50 caliber Browning M2 heavy barrel machine guns - this was the famous quad fifty.  The multiple machine guns excelled in duels with aircraft flying up to about 1,500 feet, and also provided AA fire units with local defense against ground attack or infiltration. In its secondary role of engaging ground troops, the quad fifty was evaluated post-war as "vicious and effective" when facing light armored vehicles and enemy infantry.  The reputation the weapon gained in World War II kept the quad mounts in America's fights up to and including the Vietnam War. 

The M45 was driven by a 12-volt electric motor connected to two variable speed belt-drives, one for traversing and the other for elevating the turret.  Power was supplied by two 6-volt batteries connected in series.  The batteries were charged by a 300-watt generator connected to a single cylinder, 4-cycle Briggs and Stratton gasoline engine, equipped with a self-starter.  The generator never powered the turret directly.     A nonlinear speed control system was incorporated with the belt drives in order to provide precise control of the turret at slower speeds.  This aided the gunner in tracking his target.      The M45 traversed a complete 360° circle, elevated to a fully vertical 90°, and depressed 10° below horizontal.  Solenoids fired all four M2 HB machine guns simultaneously.

Side view of the Maxon M45 turret shown without its front shield. The turret weighed about 2400 pounds with guns mounted. The quad turret could traverse and elevate at a maximum rate of 72° per second.

     The quad turret was transported by halftrack or on one of two towed mounts.  The earliest and most widespread carriage utilized the common two-ton, double-axle Army trailer.  This design was designated the Multiple Machine Gun Carriage M51 and was essentially a modification of the M7 generator trailer.  A lighter, single-axle mount was soon developed - the Machine Gun Trailer Mount M55.  This downsized version was primarily intended for use by airborne AAA units, but was also viewed as an eventual replacement for the M51.  While the M51 was usually hauled behind a 2-1/2 ton truck, the M55 was able to be towed by much lighter vehicles. 

Multiple Machine Gun Carriage M51		Machine Gun Trailer Mount M55

     The M51 was not a favorite among organizations requiring a high degree of mobility.  The carriage was often limited to well-paved roads and was not able to be quickly manhandled into position.   Some antiaircraft units, especially in the First and Ninth Army,  improvised in theater by stripping M45 turrets from the carriages so that they could be mounted more usefully on halftracks or trucks.  In the Pacific, the Sixth Army's M51 carriages were often hindered by deep sand, jungle mud and rough terrain.  However, in 90mm gun battalions or where mobility and accessibility was not a primary concern, the M51 proved its value.

     Like other antiaircraft automatic weapons, the greatest weakness of the M45 turret may have been its sighting system.  The Navy's Mark IX reflector sight was standard on the quad mount, but was best suited for engaging aircraft attacking on an incoming course - such as would be encountered on a naval vessel being threatened by torpedo bombers.  Foregoing the Mark IX, many antiaircraft units devised field-designed ring sights for their quad fifties and reported improved results.  Tenth Army AA commanders recommended ring sights capable of dealing with aircraft flying at speeds of up to 400 mph.

     Because of the limitations of the sighting system, many have questioned the firing accuracy of the quad fifty.  However, what is beyond debate is the tactical effectiveness of the weapon.  Whatever the hit ratio, the quad made a fearsome impression on both foe and friend.  Its tracer stream was often intimidating enough to cause advancing enemy ground troops to drop and freeze, or hostile pilots to break off a bomb or strafing run.  In many situations, the sheer volume of fire the quad fifty delivered was lethal enough to tip the tactical scale in favor of the Allies.  The guns' tracer display often provided American infantry with a needed morale boost.  The quad quickly earned the respect of the infantrymen it often supported, achieving for Army Antiaircraft Artillery a newfound appreciation among foot soldiers.  Veterans who fought alongside the quad mount  recall it well, with unspoken admiration showing in their eyes.  One veteran officer succinctly described the quad fifty as "a hell of a weapon."  Indeed.

M51 overlooking Wallendorf, Germany and the Sure River Valley in February 1945.  Luftwaffe pilots often used terrain features for cover.  This gunner would be waiting if a few Messerschmitts or a Focke-Wulf would try to fly low through the river valley.   Originally meant to protect the dead area of a 40mm gun or provide additional defensive capabilities to a 90mm unit, the M51 trailers were increasingly used as a standalone fire unit in the later stages of the war in both Europe and the Pacific.

The Navy Mark IX Reflector Sight      The standard sighting system on both the M45 and the twin mount M33 was the Navy's Mark IX reflector sight.  Thus, the Mark IX was found in the turrets of the M13/14 and M16 halftracks, as well as the quad towed carriages.      The Mark IX was mounted to the power turrets by a bracket connected to the crossbar that spanned the side trunnions.       In the photo (left), the sight's main optics are in the lower assembly.  Above is a lamp housing with a rheostat switch used to turn on and adjust the intensity of the lamp.  The sight's reticle was projected by the lamp. (Above) Schematic showing the concept of the Mark IX reflector sight.          Depicted here is an example of how a light bomber may have appeared in the Mark IX sight at a range of 400 yards.  For an enemy aircraft on an incoming, diving course (as on the right), the gunner merely needed to keep the center dot on the target.  The Mark IX was designed for this situation.  On a crossing course (depicted to the left), the two concentric circles acted like a ring sight.  The outer ring provided midpoint leads for aircraft traveling at 100 mph.  The inner was meant for targets moving at 50 mph.  This was a major shortcoming of the Mark IX sight.  Another ring or two, for aircraft at faster speeds, was needed.  Quad gunner peering through his Mark IX sight.

A discussion of the M33 twin mount turret is found on the M13/14 halftrack page.

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