Only four were deployed; two in the Harbor Defenses of Los Angeles and two in the Panama Canal Zone, where they could be shifted between the harbor defenses of Cristobal (Atlantic) or Balboa (Pacific).

After the close of World War I, the US Army wanted to incorporate the lessons learned from other railway gun mounts and fulfill coastal artillery requirements for hitting a moving target.

[citation needed] The primary difference from the earlier Navy versions lies in the M1920 carriage, which could be raised and lowered.

Prepositioned fixed mounts were installed at the forts, and the gun's rail trucks could be taken out from under the frame.

After the removal of the rail trucks, the gun was lowered and bolted onto a pivot point for rapid 360 degree movement, necessary for tracking ships in coast defense.