What Might Have Been… Broncos and 106mm RCLs.

On the heels of our recent post about the M40 106mm Recoilless Rifle, a reader, Dave, sends in this little morsel about a plan to mount the 106 on the OV-10.

http://www.volanteaircraft.com/images/ov-10-recoilless-rifle.jpg

The primary weapon for the Bronco was usually the Zuni 5” folding fin rocket. It packed a good punch, but it wasn’t terribly accurate, and each rocket weighed a good deal.  While mounting a 106 on an airplane would have its own weight penalty, each round of ammunition would weigh less. And the recoilless rifle would be a good deal more accurate than any rocket. And there was a plan for an autoloading weapon.

Found here, which is an interesting piece all on its own.

The Japanese Ontos?

Having discussed the Marines’ Ontos, seems only fitting to mention a very similar vehicle built at around the same time in Japan.

Type 60 Self Propelled Anti-Tank Gun

The Type 60 Self-Propelled Anti-Tank Gun (SPAT) evolved from an early 1950s requirement for the Japanese Self Defense Forces.  Emphasis on DEFENSE.  During the Korean War, the United States encouraged Japan to form a military force to defend the island nation.  The most likely threat in any conventional war was an amphibious or airborne force landing to secure the various straits connecting Russian or Chinese harbors to the Pacific sea-lanes.  As such, the Japanese needed a highly mobile force to contain a moderately armored opponent.  Requirements called for light-weight vehicles capable of rapid transport by train.  Doctrine stressed ambush type tactics to contain then throw back enemy invasions.  Concurrent projects pursued a main battle tank and a self-propelled anti-tank weapon optimized for Japanese requirements.  Both projects proceeded with some deliberation through the 1950s.

SS1-Revised Prototype with Four Rifles

SPAT prototypes from Komatzu Manufacturing (identified as MI or SS1 in some sources) and Mitsubishi Nippon Heavy Industries, Ltd (noted as MII or SS2) rolled out in 1956.  The Komatzu offering used a front mounted 105hp diesel engine, while the Mitsubishi had a 110hp engine in the rear of the chassis.  Both featured two 105mm recoilless rifles (a Japanese derivative of the US M27 recoilless rifle) in a limited traverse mounting.  After testing, Komatzu delivered an additional prototype, the SS1-Revised, with four 105mm rifles.  Mitsubishi delivered the SS-3 with five road wheels.  Then a fourth experimental batch named SS-4, with two M40 106mm Recoilless Rifles (same as used on the M50 Ontos), arrived.  The SS4 also used a more powerful 6-cylinder 150hp diesel engine, mounted in the front.  This emerged as the optimum configuration, and entered series production in 1960 as the Type 60.  In some regards, the Type 60 hearkened back to the “Tankettes” of the 1930s.

Comparison of Production Type 60 (left) and SS1-Revised (right)

Just like the Ontos, the Type 60 used .50-caliber spotting rifles to aid the aim of the main guns.  Also like the Ontos, the Japanese SPAT had a crew of three – commander, loader, and driver.  But unlike the Ontos, the Type 60’s rifles sat in a retractable turret to reduce the vehicle’s height.

Type 60 Self Propelled Anti-Tank Gun

When retracted, the turret traversed only 10 degrees left or right, with an elevation of 10 degrees and depression of 5 degrees.  Deployed in the firing position, traverse increased to 30 degrees, elevation to 15 and depression to 10.

Front View of Type 60

Note also the part welded and riveted construction. The front hull was sloped somewhat, but the sides were vertical. Overall, protection matched that of the Ontos, with only 12mm of armor to defend against small arms and artillery fragments.

Rear View of Type 60

Ammunition lockers provided six rounds. And like Ontos, the crew had to dismount to reload after firing. (And go to Toadman’s Tanks for a good walk-around of the Type 60.)

Type 60 in the Snow

In the field, the eight ton Type 60 reached 34 mph on roads. Turret retracted, the SPAT stood only 4.5 feet tall. Just over 7 feet wide and 12 feet long, the Type 60 was a compact fighting vehicle.

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Type 60 During Training Exercises

Komatsu produced over 250 Type 60s.  After the initial “Type A” production, “Type B” appeared with some structural reinforcements.  In 1974 a “Type C” entered production using a liquid-cooled engine with the same power ratings. The only other major modification considered was an auto-loader.  But that was quickly dismissed as overly complicated for the small vehicle.  As late as 2001, 140 of these SPATs remained in service.  But officially all were retired in 2008.

Type 60 on Maneuvers in 2006

Normally, I’d close out with a video or two.  But the only clips I could find feature this guy:

Occasional movie appearances were the highlight of the Type 60s service.

One might easily dismiss the Type 60 as a “knock-off” of the Ontos.  I wouldn’t be so quick.  As mentioned before, the Ontos sprang from US Army requirements for an airborne anti-tank weapon system, only later to see service as a lightweight anti-tank system for the Marines.  Designers optimized the Ontos with enemy counter attacks against envelopment operations (fancy way of lumping airborne and amphibious assault into one category).  In Japan the Type 60 was the defender countering just such envelopment.

As often occurs with weapons development, dissimilar requirements lead to very similar weapon systems.