Class S-4 shuttlecraft

The Class S-4 shuttlecraft was an aquashuttle, an auxiliary vehicle specifically constructed by the Federation Starfleet for submersible undersea operation as well as spaceflight in the 23rd century.

History and specifications
The S-4 class was an experimental shuttle type configured to explore deep oceans while having relatively similar internal control systems to the class F shuttlecraft. It featured a small power plant and specially belted and padded seats. Customized sensor arrays were specialized for underwater studies. This class of vessel was assigned for evaluation to several starships in the late 2260s. It was armed with a phaser cannon intended for defense against threatening undersea lifeforms, with firepower comparable to twice that of a phaser rifle. 

The S-4 class was designed primarily for maneuverability within a liquid, and secondarily as a spacecraft. As such, it took some experience to pilot the craft smoothly through a planetary atmosphere. The vessel was fitted with a recorder-sampler to collect data from the water. Storage lockers contained survey equipment, including tricorders and a self-powered mesh that would return samples of microbial life for analysis. The ship's window was made of a plexalloy. 

Aquashuttle NCC-1701/5A was armed with two forward phasers set at stun force, charged by a power pack. It had a hatch and could also travel on top of the water like a boat. 

Shuttles

 * NCC-1701/5A

Background

 * Geoffrey Mandel's unlicensed USS Enterprise Officer's Manual featured scale diagrams of this vessel, indicating the placement of a hatch on the port side.