A P-38 is an small-handheld engineering tool which emits sound and light frequencies designed to open wedged hatches and fused circuitry panels. They are sometimes jokingly refered to by Starfleet personnel as glorified can openers. (SCE eBook: Interphase, Part Two)

In 2368, after the USS Enterprise-D had been crippled in a collision with a quantum filament, Lieutenants Kieran Duffy and Sonya Gomez were able to jury-rig a P-38 from a gardening tool and an Elllix baffler, and rescue six trapped engineers. (SCE eBook: Many Splendors)

In 2375, when the USS da Vinci came to the aid of a crippled Pakled ship, the Pakled captain was particularly impressed with the P-38s, telling the S.C.E. crew, "You make things open; that is good." (SCE eBook: Interphase, Part Two)

According to author Keith R. A. DeCandido's annotations for Many Splendors, a P-38 was first seen in TOS episode: "The Trouble with Tribbles" (presumably the tool Kirk used to open the storage compartment), though its designation originated in Interphase.