In 1924, he returned to the States and was assigned to the Marine Corps Base, San Diego, California, where he was commanding officer of the recruit detachment and officer-in-charge, drills and instruction.

After a year as commanding officer of the naval prison, Navy Yard, Mare Island, California, he assumed duties as commanding officer, Second Battalion, Sixth Marine Regiment and in July 1936, became assistant chief of staff, Four Section, and chief of the planning section, Fleet Marine Force.

In November 1943, he became commanding general of Tactical Group One, which included the Twenty-Second Marine Regiment and certain Army units and led this organization in the assault and capture of Eniwetok Atoll, Marshall Islands, from February 6, to March 22, 1944, for which he was awarded the Distinguished Service Medal.

Fearlessly moving ashore with his men during the critical period of the landing operations, he established his headquarters near the Japanese lines and personally directed his troops with brilliant tactical skill and aggressive determination against vigorous opposition, successfully routing the enemy.

Although the division was depleted in numerical strength and physical endurance by twenty-five days of heavy fighting on Saipan, he expeditiously reorganized his forces and attained a high state of combat readiness for the subsequent landing on Tinian.

Distinguishing himself by his indomitable fighting spirit and inspiring leadership throughout these hazardous operations, Major General Watson contributed in a large measure to the success of the vital Marianas Campaign.