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John R. Haynes Mark 4 20mm Write-Up
Alex Johnson


Many PT Boat modelers tend to focus on the armament carried by boats in the gunboat role. These weapons include the two lightweight 20mm Oerlikon mounts, the two versions of the automatic 37mm aircraft guns and the 40mm Bofors cannon. We should not forget that as late as 1943, both Elco and Higgins boats came factory-equipped with 20mm cannons on the Mark 4 mount. This standard US Navy base consisted of a heavy cast conical base, shoulder rests and an armored shield. While the mount was not well suited for small craft application due to its heavy weight of 1,695 pounds, the Mark 4 was used on second-series 77' Elco boats and early 80' Elco and 78' Higgins boats. Luckily for the modeler, John R. Haynes makes the Mark 4 gun kit and it is an excellent product which will be welcomed by builders of many types of small combatant vessels.


The package contains cast parts and a photo-etched brass sheet. The cast gun kit comes in three pieces: the gun body, the elevation wheel and the tripod base. The gun body is fully detailed with breech, barrel, ammunition drum and sight. The elevation wheel was used to raise and lower the gun depending on the angle of the target. In service the gun was kept in the lowered position when not in use and while engaging surface targets. It was raised when engaging aircraft to allow the gunner to aim from a standing position instead of a crouched position. The mount consists of a conical base and yoke or cradle. All three cast parts are well-detailed and contain little "flash." The photo-etched brass sheet includes shoulder rests, two sight rings and an armored shield. When compared with photographs and drawings of the real thing, no detail is omitted.


The cast gun parts required minimal preparation and took only several few minutes to be readied for assembly. With a little filing and sandpapering, the few edges from the molds were removed. The armored shield and its bracket are made of a single photo-etched brass part which folded easily into the proper position. I attached the shield to the yoke using CA glue and proceeded to secure the elevation wheel to the conical base. The last few steps were to attach the ring sight and the two shoulder rests. I now had two subassemblies which would receive separate colors. The mount and shield would be the color of the boat while the gun itself would be painted Gunmetal.


Painting was almost as easy as the preparation and assembly. I prepped the surfaces with gray Krylon primer and allowed them to dry. The mount and shied were painted gray and the gun itself was painted with Testors Model Master Gunmetal. It was a simple matter of shooting the parts with my airbrush which really brought out the detail of the various components.

Final Assembly

Once the paint dried, I attached the gun to the mount using CA glue. I chose to have the gun at a level elevation. Based on photographs, this appears to have been the common locking position for Mark 4 mounts when not in use. Besides, with the shield and barrel, that position gives the gun an aggressive look. The Mark 4 mount may have been heavy but it sure looked tough. Just because a weapon did not turn out to be the ultimate gun mount doesn't mean it can't make an interesting modeling subject.


This Mark 4 20mm gun kit by John R. Haynes is excellent. By my estimation it is fully accurate and it was a joy to assemble. The modeler can have a stunning piece of armament in almost no time, although the observer might think it took many hours based on the detail and quality of the cast and photo-etched parts. This gun kit is that good. Modelers of second-series 77' Elco boats and early 80' Elco and 78' Higgins boats will find this product useful. It will dress up any early-war PT Boat which used the Mark 4 mount. Interestingly, one of my previous models used the Mark 4 for a truly unique application. In September of 1943, the crew of PT 155 of RON 9 in the Solomons replaced their aft 20mm gun with a salvaged M4 37mm aircraft gun. With slight modification to the yoke, the gun fit right onto the old Mark 4 base. Whatever one's needs, this gun kit by John R. Haynes will find its uses on many projects.