There are several scenes in which service personnel are wearing their hats while indoors. But regulations stipulate that when entering a building one was to remove their cover, and only place back on their heads when leaving that structure.
When Lt. Col. Black and Lee are returning from the destroyer in the harbor, the entire area is lit up as if it was peacetime, despite New Caledonia being a major U.S. Navy base in a war zone.
The US Army Air Force C-47 cargo planes are painted in post WWII paint scheme rather than the wartime green. When the Air Force became a separate service in 1947 the white over bare metal paint scheme as seen in the movie was adopted.
When Lee leaves New Caledonia, the Skytrain she boards has post war US insignia. The US insignia on the Skytrain had a center red stripe on the white bars. But those red bars would only come in January, 1947, almost a year and a half after the war ended.
The year is 1943, but all of Deborah Kerr's hair styles, clothing, and the style and cut of her uniforms, is strictly 1955.
About an hour into the film, Lt. Col. Black and Lee are in a jeep and they pass a sign saying "Fleet Hospital 109". U.S. Navy Fleet Hospitals were not numbered as such - three digits beginning with '100' - until 1944. Additionally, Fleet Hospital 109 was in Brisbane, Australia. New Caledonia had Fleet Hospitals 105 and 107.