2011 October 5 update: Forward turret updated to Elco drawings and aft turret added. Turret step updated.
2010 March 22 update: Turret step, as found on the side of the chart house and day room, added.
2009 September 29 update: Redrawn forward turret added.
The following images show dimensions and placement for Elco PT 103-196 and 314-367 turrets, and their steps. These dimensional images represent a best effort on my part, please confirm dimensions given here for yourself if errors cannot be tolerated. Images are for non-commercial personal use only, please obtain permission for any other use.
The following are selected turret related sections from the Navy PT boat build manual found at http://www.hnsa.org/doc/pt/specs/index.htm. Please note that this manual is a later version than the 103 class, read coverage notes below the title. Turret base cylinder diameter on the earlier boats is 44":
DETAIL SPECIFICATIONS FOR BUILDING MOTOR TORPEDO BOATS
FOR THE UNITED STATES NAVY
BUREAU OF SHIPS
31 March 1944
NOTE: The Detail Specifications are based on Specifications for Motor Torpedo Boats PT 103 to 138 design No. 80-N-3 (dated 2 January 1942) and addenda thereto (dated 22 February 1943), as prepared by Electric Boat Company, Elco Naval Division, Bayonne, N. J., with the minimum modifications made by the Bureau of Ships to make the hull specifications applicable to PT 565-624 Class.
Detail Specifications For Building Motor Torpedo Boats, March 1944, provides the builders specifications for PT 565-624.
Nonskid treads shall be added to firing steps in both machine gun turrets.
Four .50 cal. A. A. machine guns in two mounts, Mk. 17 Mod. 1.
The contractor shall furnish and install suitable depression stops for .50 cal. A. A. machine guns to give approved clearance of structure, personnel on bridge, etc.
It is unnecessary to dismantle turrets in removing either engine or tank hatches.
Machine gun turret cylinders shall be 48 inches 0. D. and be located as per plan and constructed of molded plastic plywood, with special connections to after trunk and chart house. Top shall be designed to carry government furnished scarf ring gun mount for twin .50 cal. machine guns. Scuppers to deck at low point of base. Firing steps for depressed fire shall be fitted.
Stowage for .50 cal. ammunition shall be provided in crew's dayroom under settee on port side, and in locker on starboard side of bridge, with outboard door, forward of the machine-gun turret. Stowage shall be provided for four boxes of ammunition.
Access to the after machine gun turret shall be through a door cut in the part of turret wall rounding out from the port aft corner of the day room.
The sides and top of day room trunk shall be constructed as described in section O-1, and shall include the after port .50 cal. machine gun turret, with main and depressed firing floors, limiting stops, exit door, and adequate drainage, as per plan.
Machine gun limiting stops of brass or steel tubing shall be fitted as required to prevent accidental firing into ship or occupants of bridge (see section A-5).
GRAB RODS AND RAILS.
Grab rails as per plan shall be of wood or brass pipe in bronze stanchions. Special grabs shall be fitted at ladders, companionways, hatches, and elsewhere throughout ship as required for safe passage on deck or below.
Two canvas covers shall be provided for .50 cal. machine gun mounts to completely enclose guns, mounts, and limiting stops. After turret to have separate spray shield to height of limiting stop.
All covers shall be fitted with proper lashings.
All canvas covers and life preservers to receive approved treatment for fire retardance.