From Halopedia, the Halo wiki
The Sentry autocannon is a line of naval coilguns used by the UNSC Navy during and after the Human-Covenant War.
The M60 Sentry was a variant of the Sentry autocannon mounted on the Diligence-class light destroyer, Hillsborough-class heavy destroyer, and the Vindication-class light battleship.
The M66 Sentry was mounted on the Epoch-class heavy carrier and Autumn-class heavy cruiser. The UNSC Pillar of Autumn was also retrofitted with them in preparation for Operation: RED FLAG.
A close up of a M66 Sentry on the Pillar of Autumn.
Naval coilgun (LNT-450 • Castor) • Naval coilgun battery (11A2R1 • Mark 15 Breakwater • Spitfire) • Sentry • Gauss cannon (M65 • M68 • M68B • M70) • M92 Principle Gauss Cannon • Mini-MAC • "Super" MAC
Mass drivers: Onager (Mark 2488 • Mark 2551) • Ballista