Uses the same gun-mechanism of the 20 mm Vulcan Phalanx Block 0 weapon system but on a much simpler mounting. Used primarily on Patrol Gunboats. Manufactured by Sumitomo Heavy Industries, Ltd.

Gun Characteristics

Designation 20 mm Machine Gun JM61-M
20 mm Machine Gun JM61-RFS
20 mm Remote Control Machine Gun JM61R-MS
Ship Class Used On JM61-M: MSC Hatsushima, MSC Uwajima, MSC Sugashima, MSC Hirashima, MSC Enoshima, MSO Yaeyama and LCU No.1 classes
JM61-RFS: PG No.1
JM61R-MS: MSC Enoshima (MSC-606 Hatsushima), MSO Awaji
Also used on Japan Coast Guard Vessels
Date Of Design N/A
Date In Service about 1990
Gun Weight N/A
Gun Length N/A
Bore Length about 59.8 in (1.520 m)
Rifling Length N/A
Grooves N/A
Lands N/A
Twist N/A
Chamber Volume N/A
Rate Of Fire 450 rounds per minute cyclic


Type Fixed
Projectile Types and Weights APDS Mark 149 - 0.22 lbs. (0.10 kg)
APDS Mark 149-2 - 0.22 lbs. (0.10 kg)
APDS Mark 149-4 - 0.22 lbs. (0.10 kg)
Bursting Charge N/A (Solid Shot)
Projectile Length 6.62 in (16.8 cm)
Propellant Charge N/A
Cartridge 20 x 102 mm
Muzzle Velocity 3,650 fps (1,113 mps)
Working Pressure N/A
Approximate Barrel Life N/A
Ammunition stowage per gun N/A
  • The sub-caliber penetrator of the Mark 149 is 0.502 inches (12.75 mm) in diameter.
  • The Mark 149 projectile was developed to provide a significantly increased anti-armor capability, optimized exterior ballistic performance and short time-of-flight over the previous Mark 50 round. The original Mark 149-2 projectile was a depleted-uranium sub-caliber penetrator. In 1988, the US Navy switched to the Mark 149-4 which uses a tungsten penetrator. The change over to tungsten was in order to reduce radiation exposure to personnel and to lessen the environmental impact. Tests with the tungsten penetrator showed acceptable results against likely missile and aircraft threats. The Mark 149-4 round includes a red tracer.
  • Ammunition is supplied in 100-round belts.


Range of APDS projectiles
Elevation Range
45 degrees 4,900 yards (4,500 m)
Maximum effective range 1,625 yards (1,490 m)

Mount/Turret Data

Designation N/A
Weight N/A
Elevation -20 / +80 degrees
Rate of Elevation N/A
Train 360 degrees
Rate of Train N/A
Gun Recoil N/A

Other Resources

For photographs of the JM61R-MS version, see the Mine Sweeper Coastal MSC-606 website.


"The Naval Institute Guide to World Naval Weapon Systems 1991/92" by Norman Friedman
"JSDF Equipment Yearbook 2002-2003"
US Navy Press Releases
Raytheon Systems Company Press Releases
Main Naval Armament website
Special help from Hiramatsu Shun'ichi

Page History

22 February 2006 - Benchmark
27 May 2012 - Updated to latest template
26 September 2016 - Converted to HTML 5 format
16 June 2019 - Added additional details