Castle in the Sky (originally known as Laputa: Castle in the Sky, itself named after the floating island Laputa in Gulliver's Travels, but re-named for the American release due to this having a rather unfortunate meaning in Spanish) is a 1986 anime film directed by Hayao Miyazaki and is the first film from Studio Ghibli (Porco Rosso, Lupin III: The Castle of Cagliostro).
The following firearms can be seen in Castle in the Sky
Dola and her pirate gang all use single barrel break-open grenade launchers that fires explosive and gas rounds. Pazu obtains one from Dola when he goes to find Sheeta.
Gatling Gun
In the first Scene Where Dola and her gang raid an airship, two crewmen fire a hand-cranked Gatling Gun.
Webley Mk VI
The Army, Muska, and the other secret service agents carry Webley Mk VI revolvers as their standard service sidearm.
Hybrid Short Magazine Lee-Enfield (SMLE)
All of the soldiers seen in the film carry hybrid SMLE bolt-action rifles, due to the slightly longer barrel of the No. 4 rifle and Gewehr 98 Lange-Visier sights. The rifles are depicted with five round magazines instead of the better known ten round magazines, which is plausible since the Lee Enfield's magazine could be detached and swapped in the field, thanks to the small lever in the trigger guard.
Lee Enfield No.4 Mk1
Surprisingly, a genuine Lee-Enfield No.4 Mk1 used by one of the sailors in the passenger airship in the beginning.
Maxim M1910
The fort's arsenal includes a Maxim M1910, which is used to try to fend off against the Laputian robot.
At one point the army pulls up an armoured train, the front car of which is essentially a WW2-era German armoured railway car with additional casemate guns based on the 6-pounder Hotchkiss guns of WW1 British "male" tanks.
Fortress Tedis Cannons
The Fortress Tedis has several short-barrel heavy cannon turrets built on the outer walls of the fortress. These appear to be based on WW1-era retractable fortress cannon cupolas, such as those mounted on the French fortresses at Verdun.
Air Destroyer Goliath
The Army's "Air Destroyer" Goliath is armed to the teeth with massive cannons, as well as several Maxim MG08 machine guns for anti-air defense purposes.