The 12 inch vent with a valve to shut it off in case of a gas attack. This one is full of garbage that people have dropped in from above. The hot water pipes go through the wall into the OBS Booth, so there would have been a radiator up there too. While Coast Artillery Museum volunteers were clearing more brush in front of the GPMTCP in the summer of 2012 a very heavy cast iron steam radiator was found on the slope, it almost certainly came from this building.

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