My guess is that the film was shot on the 16th when there were plans to have the ANZAC force support Lexington’s raid on Rabaul. That did not end up happening because there was not enough fuel available to fuel up both the Lexington’s task force and the Australian ships.
Lexington did not lose her 8 inch mounts until after she returned to Pearl in late March.
You're right.... The footage was all (supposedly) shot from the Lexington. This makes me wonder if it was not shot from Hobart instead, because the shot of the motor launch approaching the filming vessel is clearly one which shows two "large" caliber guns trained outward.
The USS Lexington had her 8 inch guns replaced by the quad 1.1 inch light AA guns before the Battle of the Coral Sea. The only ship on the Allied side with twin 8 inch turrets was the HMAS Australia. HMAS Hobart was also present and would have had twin 6 inch turrets.
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