Controllably, the chamber may be filled either with {TAIL ~ air} from {HEAD ~ an external source} of pressurized air or may be allowed to flood through the channel with water from the surrounding body of water 
Controllably , the chamber may be filled either with { TAIL ~ air } from { HEAD ~ an external source } of pressurized air or may be allowed to flood through the channel with water from the surrounding body of water
OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH