Proton cannon

This caption is above 'Get off my lawn!' jokes, as are you.

Proton cannons are a type of weapon emplacement used to combat the threat of enemy starships.

Fiction

The Transformers cartoon

The Quintessons had a massive proton cannon that was used to defend Quintessa from invaders. The Aerialbots arrived on the Quintesson homeworld in order to rescue their fellow Autobots trapped on it which prompted the Allicon guards into firing their proton cannon at the Autobot fleet. Whilst initially doing damage, Silverbolt sent Air Raid and Skydive to take out the cannon. Five Faces of Darkness, Part 2

Armada cartoon

After being upgraded by the Mini-Cons, Starscream's null laser cannons were replaced with proton cannons, which he used in a futile effort against Unicron, though the blast was powerful enough to breach Cybertron's atmosphere and nearly reach the monster planet. Cramp

2005 IDW continuity

The Functionist Universe

In an alternate timeline, Megatron and the Anti-Vocationist League found themselves defending the city of Adaptica from Luna 2, repurposed as a giant harvester unit. When Megatron asked about defences, Nine-of-Twelve glumly informed him that they only had a few proton cannons and missile launchers. Megatron made the best of the situation by ordering Anode to deploy the weapons where they would do most damage, and Nine-of-Twelve to lead the people underground via multiple routes. Bad Moon Rising