Paul Whitman




One of the more curious but practical weapons of the SWPA was the 60mm Petzelt Low Trajectory Mortar.

The light weight and quick set-up of the M2 60mm mortar made it an excellent indirect fire support for fast moving and lightly armed Paratroopers.  Its weakness in jungle terrain soon became evident to the mortar platoons training in northern Queensland. In areas where there was limited visibility due to tree cover, and particularly where there was a thicker jungle canopy, the indirect lobbing trajectory of mortar rounds became a less effective weapon.

The Japanese infantryman had their Type 89 Leg Mortar, which fired a 50mm projectile.  This muzzle-fed, trigger fired rifled weapon was widely used by the Japanese. It could be used by an individual soldier, although it was allocated to a three-man section.  Light enough to be placed in a carrying case which was then strapped to a soldier's leg,  an unfortunate translation of the title saw it called the "Knee Mortar" and the name stuck.

The Type 89 had benefits in jungle areas that theM3 60mm Mortar did not. As well as ease of carriage, it could be aimed on a shallow trajectory (less than 45 degrees, if propped against a strong backstop to protect the operator), and fired with decent accuracy directly towards the target. Range was achieved by an adjusting nut that moved a rod up and down the rifled barrel. It was fired by pulling on a leather handle attached to the trigger.


 In early combat with the Japanese, the flexibility of the Type 89, and its lethality became evident to all who faced them.   Considering that the M2 Mortar's high trajectory was a disadvantage, Staff Sgt. Norman F. Petzelt  developed a "knee mortar like 60mm mortar" that could be safely fired at a very low angle. His first designs were developed in Gordonvale in late 1943, and his prototypes were built shortly afterwards when the 503d were training in staging areas of Port Moresby.  Pfc Andrew P. Silvas assisted Petzelt in the development. 


Essentially, Petzelt modified the base plate with a swing arm leg that could be easily emplaced to steady the mortar and control recoil when engaging targets horizontally. The mortar could not be "drop fired" in the conventional manner, so he designed a trigger activated firing pin mechanism. The barrel would be supported in the hands and aimed directly at target without the necessity of a sight. It was crude, simple and deadly.


After successful proof of concept firings,  the officers of the 503d quickly saw the advantages of Petzelt's efforts,  and they supported the modification of a number of the mortars. One was allocated to each Company.  It could be fired in the same manner as the normal M2, so it was not a replacement for the M2, simply an improved version of the tried and true formula. In an effort to see series production of the "Improved Mortar,"  Petzelt, with the support of the 503d PIR, submitted drawings  to the War Department Ordnance Division whilst the 503d was stationed at Camp Cable, south-west of Brisbane in February 1944. There was no response.

Development wasn't always smooth.  Bill Calhoun recalls that Cpl. Burl Martin was required "to leave his stripes on the desk" when Martin managed, in a test-fire of bushings which might allow flares to be fired, a conflagration of  the E Company's Supply tent on Noemfoor resulted from a direct hit. Clearly, Lt. Bill Bailey didn't buy that the incident was due more to the alcohol Martin was drinking than the inaccuracy of the mortar, "and thus Burl became, once again, Private Martin."*


In combat use, the Petzelt mortar was very successful.  It was used, but not needed at Nadzab and Mindoro. It was needed and used on Noemfoor where, Petzelt writes,  the official count of enemy dead was 30.  On Corregidor, it was used to good purpose in placing grenades into the mouths of tunnels and holes, without the necessity of approaching them too closely. It was used on the attack upon the Ordnance Machine Shop, though this action was had to be brought to a close by bringing in a 75mm Pack Howitzer, and direct firing it through the Shop's metal windows and doors.  Of the body count on Corregidor, Petzelt went on to say, "No one was damn fool enough to go into any cave to count anyone."


Petzelt had hopes for the adoption of his improvement to the Mortar, and so did the the officers and men of the 503d, who had given it a thorough road testing, and had found it commendable.  Petzelt's later drawings contained the signed support of  a number of luminaries, including Col. John H. Davis, Brig. Gen. George M. Jones, and Lt. Gen John J. Toland III, as well as  Capt. John H Blair III, who had commanded I Co in 1945.  A set of its blueprints remained one of Jones' prominent sentimental souvenirs until his death.


But history takes many paths and unfortunately for Norman Petzelt, the concept of the low trajectory capable mortar was not to be, as the bazooka would be further developed, and the RPG would fulfill the need.


Our efforts to date have failed to uncover any photograph of the Petzelt Mortar.


Petzelt Estate - Courtesy of the Reference Services, Hoskins Library, University of Tennessee, Knoxville, Special Collections Library,











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Bill Calhoun recalls:

"I became well acquainted with the Jap "knee mortar" the first night on Corregidor when Freihoff  and Huff were trapped in the magazine in Btry. Wheeler. I went to Bld. 28-D to get a flame thrower team to Wheeler. Once this was arranged, I started back. As I crossed the open space approaching the hill forming the berm, a Jap 50 opened up. I ran to the end of the berm and sat leaning back against the hill with my legs stretched out across the small drainage ditch. A knee mortar shell dropped between my legs into the ditch. I received several small mortar fragments in the face and chest which were never treated.

I believe Sgt Petzelt jumped in a stick after the deadly stick.   Fitzhugh Milligan tells of seeing Petzelt his a cement wall so hard, they thought he must be dead or badly injured. However, Petzelt jumped up and ran to the assembly area.

We loved our direct fire mortar and used it. Henry McCory's had it. He was really good with it, but it caused his death. As were attacked the ridge on Negros we moved in  a line of skirmishers. I was in the middle as company commander. Karl Sneider, a company runner was next to me on the left. I had Henry next to me on my right because I expected to use the direct mortar to fire into the Jap bunkers and caves. He was good with the weapon. His squad trailed just behind us. The opening blast of MG fire killed both Schneider and McCory. I was amazed to be untouched.  This was my second deliverance - back on Corregidor, Feb. 22nd, in Grubbs Ravine at RC6 my runner next to me and Paul Narrow next to him, were killed by an opening blast.

I'll have to inquire further about this when I next see Burl Martin. I believe he may have been fooling with our direct fire mortar when he accidently fired a flare and got a direct hit on E Co.'s supply tent  back at Noemfoor. It made a good fire. Bailey called Martin into the CP tent and told Cpl. Martin to leave his stripes on the desk even though it wasn't the alcohol he was drinking, but he was experimenting with trying to bushings with which flares could be fired from the mortar. Bailey didn't buy it, so Burl became Pvt. Martin."

pia Bill