Why navies return used Rolls-Royce gas turbines

Do navies lease Rolls-Royce engines rather than own them?

Not exactly; the navy buys the engine, while Rolls-Royce may later buy it back so the company can study wear and service-life damage.

Ownership is separate from the manufacturer's interest in retrieving an engine after service. The purchase price can account for a later buyback, allowing Rolls-Royce to inspect long-term damage and feed experience into future engineering. The result may look like a lease from the outside, but the underlying transaction and technical purpose are different.