The M20 was a French submarine-launched ballistic missile (SLBM) deployed on the nuclear Redoutable-class submarines from 1977.

The M20 was the third member of the MSBS (Mer-Sol-Balistique-Stratégique, "sea-ground ballistic strategic") family which comprised a number of submarine-launched, intermediate range missiles.

Logistical support for the MSBS fleet is provided by the Île Longue Naval Base in Brest Bay, where the assembly and storage facilities for maintenance of readiness are located.

[1] The M-20 was a two-stage, solid propellant, intermediate-range ballistic missile, 10.4 m in length and 1.5 m in diameter.

The payload was believed to include some penetration aids and the single re-entry vehicle had some hardening against nuclear effects.