Spartan Gold: stalactite and more

pg 156 Hanging from the ceiling in the far corner was what he'd initially taken for an especially long stalactite.

A stalactite (UK /ˈstæləktaɪt/, US /stəˈlæktaɪt/; from the Greek stalasso, (σταλάσσω), "to drip", and meaning "that which drips") is a type of speleothem (secondary mineral) that hangs from the ceiling of limestone caves. It is a type of dripstone. The corresponding formation on the floor of the cave is known as a stalagmite.

essentially a pair of G7e torpedoes stacked atop one another

The G7e or more appropriately the G7e/T2, G7e/T3, and G7e/T4 Falke torpedoes were, with the exception of the T4 model, the standard torpedoes for Germany during World War II. All of the G7e models shared standardized dimensions for all German torpedoes designed for use by U-boats during World War II, they measured 53.3 cm (21 inches) in diameter, 7.16 m in length, and carried a Schießwolle 36[1] (a mixture of explosives) warhead of 280 kg. All were powered by 100 hp (75 kW) electric motors and lead-acid batteries which needed constant maintenance to maintain their reliability. Additionally, the batteries of these torpedoes needed to be preheated to a temperature of 30 °C (85 °F) to operate with maximum speed and range, though generally this was a non-issue as U-boats had the element of surprise and often had the advantage of firing the first shot.

converted into a cockpit/battery compartment with an acrylic-glass viewing dome

Poly(methyl methacrylate) (PMMA) is a transparent thermoplastic, often used as a lightweight or shatter-resistant alternative to glass. It is sometimes called acrylic glass. Chemically, it is the synthetic polymer of methyl methacrylate. The material was developed in 1928 in various laboratories, and was first brought to market in 1933 by the Rohm and Haas Company, under the trademark Plexiglas. It has since been sold under many different names, including Lucite and Perspex.