What is the name of Rolex's first waterproof watch?

Rolex’s first waterproof watch was the Oyster.

Introduced in 1926, the Oyster used a hermetically sealed case to protect its movement from water and dust. Its bezel, case back and winding crown screwed down against the middle case, creating the foundation of Rolex’s long-running Oyster case architecture. Hans Wilsdorf chose the name because the watch was meant to remain protected underwater like an oyster’s contents.

Rolex publicized the design dramatically in 1927, when British swimmer Mercedes Gleitze wore an Oyster during her English Channel swim. After more than 10 hours in the water, the watch was reported to be working properly. The event became one of the earliest major examples of a brand using a real-world endurance feat to demonstrate a watch’s reliability.

The name can cause confusion because “Oyster” later became part of many Rolex collection names, including Oyster Perpetual and Oyster Datejust. Rolex had also experimented with an earlier watch called the Submarine in 1922, but it was the 1926 Oyster that became the company’s landmark waterproof wristwatch and the canonical answer to this question.