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Detail of the forward hatch.

The three electrical connectors in a triangular pattern are in the approximate location of the tracking light.

My understanding is that the forward hatch was initially round so that the LM crew could dock with the command module upon returning from their lunar journey; it would be much easier for the crew to dock with the CM in front of them (using the forward hatch), rather than with the CM above them (using the overhead hatch, as was used during the actual missions).

With this in mind, I'm unclear as to why the bottom of the hatch is flattened off. LTA-3 clearly dates from a time after docking with the forward hatch was abandoned (there's an overhead docking window). Perhaps the hatch is still round just "because it's always been that way."