What is the small contraption front centre of the picture - it appears to be a frame with four small sets of tracks. The 'T' handle suggest it is manpowered but there is also a ring that suggest a rope or chain could be attached but no vehicle tow attachment is visible.
I'm assuming its a frame to move an aircraft or component on soft ground.
This is the Bomb & Torpedo Skid Mark 6, for use on soft ground, of American manufacture. Location is Emirau, probably 1945. This skid, to quote Ordnance Pamphlet 865, "has a cradle body similar to the Mark 5, but is carried on 4 track-laying wheels by a yoke at each corner of the body. Each yoke is supported by one of 4 short axles specially provided for this skid. Each axle carries one Track Laying Wheel, Mk. 1. The capacity of the Mark 6 is one bomb, or torpedo of the Mk. 13 series, up to 2,500 pounds in weight. It is designed for advance base operations, and several skids may be pulled in a train when suitably connected. The two forward track-laying wheels are steerable, being held together by a tie-rod connecting the wheel-yoke extensions", (etc, etc). Overall dimensions (excluding drawbar) are 55 inches length (105 inches including drawbar), by 36.5 inches width by 19 inches height, and weight is 550 pounds. Stock Number for this unit is 3-S-3091. And yes, those are F4U-1Ds of 5 SU in background.