“Tom Swift and His Diving Seacopter” by Victor Appleton II

Is it a helicopter or a submarine? It’s both! Tom Swift Jr.’s amazing Seacopter can fly through the air and dive deep beneath the waves. Tom and Bud Barclay plunge into an undersea mystery, with dangerous enemies close behind. This is Book 7 of the series, and the hardcover is in good vintage condition at Dead Tree Dreams.