|A horse, indeed, under water|
It seems that no modern energy storage system, never mind a 1945 system, could allow such a device to surface every 12 hours. Len doesn’t go into details but I assumed that such a machine would be like a small submarine with a floodable chamber to make it sink and a compressed air cylinder to clear that chamber of water to make it surface again. The air cylinder would then have to be replenished, on the surface, ready for the next dive/surface cycle 12 hours later. So the system would need either a diesel engine or a large electric motor in order to recharge the compressed air tank. Either way the required supply of diesel, and/or battery power stretched my credibility.
However, the image of this tireless machine traveling twice a day from the sea bed up to the surface is really too striking to abandon. So it’s fun to speculate what the Horse in the ‘lost‘ Harry Palmer film would be like. So when was the book set? Having retrieved the thing they have to chisel a couple of bolts off, ‘but that’s only to be expected after more than a decade under water’. So, is there a way to keep a submersible weather buoy going until 1963, when the book was published?