20mm Machine Cannon
 
The last line of defense weapon against airplanes. 
A maximum range of 10,000 feet, an attacking airplane traveling at 250 mph was 28 seconds from hitting you.
Effective range was much less and so was the time to impact.
  The pedestal mount was used aboard TEXAS through the Aug 1944 Invasion of Southern France. In the Pacific, in 1945 a tripod mount was in use.   The 60 round ammo drum could be fired empty in 8 seconds   The bag between the gunner and the pedestal collected the shell casings of fired shells.  
The gunner is looking through a Mark 14 gun site, of which 20 were installed in the late summer of 1943, with only two on the main deck guns
 
  4 Configuration Periods   
  1942 Mar-May 1942 Aug 1943 Jun 1944 Oct 1948 on
Crane . .2  0 . .
Superstructure Deck . .2  0 . .
Foremast - Flag Bridge 4 4  0 . .
Mainmast - 20mm platform (top) 4 4  0 . .
Mainmast -Searchlight 20mm platform 2 2 2 0 .
Mainmast - new 20mm platform . . . 4 .
Turret 2 & 4 - top of . . 12 (6 ea) 12 .
20mm Clipping Rm - main deck . .  4 4 .
Main Deck 4 24 24 24 8
TOTAL 14 38 42 44 8
 
  Period 1 of 4:  March-May 1942 thru August 1942  
 
Source is combination of two letters.
6 August 1942 clipping room letter that  24 more being installed
22 Sep 1942 clipping room letter that 38 20mm were aboard.  (Deduction, 14 were aboard prior to the August-September install of 24 more at Norfolk Navy Yard).
Date Installed is a deduction.
The possible dates were December 1941 - 6 January, in Argentia Naval Base, Newfoundland or one of two 1942 periods in the Norfolk Navy Yard of March or April- May. Newfoundland, Argentia seems the least likely possibility.
  Foremast - 4
Flag Bridge
  Mainmast - 6      
    Level 1
  Level 2 Searchlight Platform
 
Main Deck - 4
 
  Period 2 of 4:  August 1942 thru May 1943  
Source - two letters. 6 August 1942 clipping room letter 24 more being installed.  22 Sep 1942 clipping room letter of 38 aboard. 
  Foremast - 4
Flag Bridge
  Mainmast - 6      
    Level 1
  Level 2 Searchlight Platform
 
 
  Crane - 2   Superstructure - 2   Main Deck - 24 (added 20)  
   


 

 
  Period 3 of 4:  June 1943 thru September 1944  
Source: 8 July 1943 letter alterations to effect improvement to the AA defense stating 42 guns were aboard. Photos 15 March to 30 May 1943 show no additional 20mm guns.   This leaves only the June 1943 period in the Boston Navy Yard for the installation.
 
Main Deck - 24
 
  Mainmast -2
Searchlight Platform
  Added
Turret 4 - 6
Clipping Rm - 4
  Added
Turret 2 - 6
 
    Clipping Rm on maindeck
 forward of Turret 4






 







 
 
  Period 4 of 4:  October 1944 on  
In the New York Navy Yard the mainmast platforms were replaced. The two 20mm on the Searchlight Platform were relocated to the new 20mm Gun Platform above the new Searchlight Platform with two more installed
Main Deck
             
  Mainmast - 4 (2 added)
new 20mm Platform
(second level from the bottom)
  Turret 4 - 6
Clipping Rm - 4
  Turret 2 - 6  
       
  Magazines - 2nd Platform  
Only one magazine (gray-aft) with a capacity of 225,000 rounds. 
Hoists brought the shells up to the 2nd deck and inboard of the CPO Washroom (starboard) and CPO Water Closet (port)

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