Before joining VT-1 Petty Officer Nielsen was assigned to VT-100 at Barbers Point Oahu where he presumably received training in SB2C Hellcat and/or TBF/TBM Avenger aircraft.

On June 2nd 1944 ARM3c Hans Raymond Nielsen reported aboard the USS Copahee (CVE-12). The Copahee departed Pearl Harbor the next day carrying replacement aircraft and military personnel heading to the Marshall and Marianas Islands.

On June 14th 1944, after about 12 days and some 4000 miles traveled, Petty Officer Nielsen was delivered aboard the USS Yorktown as a "replacement air crewman". The USS Yorktown had just completed three days of combat off of Guam and was heading north toward the Bonin Islands (Chichi Jima and Iwo Jima). VT-1 had already lost one aircraft (Lt Merrell) and would lose another the next day at Chichi Jima (Ltjg Keeler).

The names of the VT-1 pilot and gunner that he flew with are not known.

USS Copahee (CVE-12) muster report June 3rd 1944

USS Copahee (CVE-12) muster report June 21st 1944

Hans Nielsen (1924)