These weapons might not do the most damage, but they are the biggest ever made in history. You haven't lived until you've seen a tank the size of a small house.
The largest tank ever made: the French Char 2C (also known as FCM 2C), developed during WWI, used between 1921 and 1940. Only 10 were built.
This 69 ton tank was 33 ft 8 in (10.27 m) long, 13 ft 5 in (4.09 m) high and 9 ft 10 in (3 m) wide and had a 75 mm gun and four 8 mm machine guns.
(via Wikimedia Commons and worldwarphotos)
Two 36 inches (914 mm) caliber mortars, never used in combat: the British Mallet's Mortar (only 2 were built in 1857, designed by Robert Mallet) and the American Little David
The 11 feet (3.35 m) long Mallet's Mortars weigh 42 long tons (42,674 kg), and had 1.25 long ton (1.27 t) cartridges.
The 40 ton Little David was used for test firing aerial bombs during WWII. It had a 22 ft (6.7 m) long barrel and could fire 3,650 pounds (1,656 kg) weigh shells.
In 1944 it was converted into a siege mortar: the 80,000 pounds (36,000 kg) and the 93,000 pounds (42,000 kg) base were transported by two artillery tractors, and could be ready to fire in 12 hours.
(via Wikimedia Commons 1 – 2 – 3)
The M388 Davy Crockett, a short-ranged recoilless gun, to firing the M388 nuclear projectile. Its production began in 1956, tested between 1962 and 1968, but deployed with US Army forces from 1961 to 1971.
According to Military Factory:
The entire projectile weighed 76 pounds and was 2 feet, 6 inches long with a diameter of 11 inches. The W54 warhead portion encased in the projectile weighed 51 pounds. The weapon had an automatic lethal radiation exposure radius of 10,000 rem out to164 yards (150m) at the blast site and a delayed fatal dose of 600 rem within 150 yards (137.16m) of the blast center - of course this was all dependent on wind direction.
The world's largest bombard by caliber: Tsar Cannon, created in 1586 by Andrei Chokhov, now displayed in the Moscow Kremlin. The 19.5 ft (5.94 m) long weapon has a caliber of 890 mm.
(via Dave Nicoll and eimoberg)
The most powerful thermonuclear weapon ever detonated: the Tsar Bomb, released over the Mityushikha Bay testing range, Novaya Zemlya archipelago, Soviet Union, on October 30, 1961. It had the yield of 50-58 megatons of TNT, made a fireball, about 5 miles (8 km) in diameter and totally destructed everything in a circle 44 miles (70 km) in diameter.
(via Nuclear Weapon Archive)
A .950-caliber rifle, the largest centerfire rifle ever made with the biggest cartridges, developed by SSK Industries. Only three were made.
Typhoon-class nuclear submarines, (also known as the Project 941 or Akula) the largest class of submarines ever built. Six of them were launched, between 1980 and 1988, but now all of them are retired, and three were scrapped.
All six ships were 574.15 ft (175 m) in length.
(via Dmitry Lovetsky/AP)
The largest-calibre rifled weapon ever used, with the heaviest artillery shells: Schwerer Gustav and Dora, two railway guns weighed 1350 tons, designed and built by Krupp in the late 1930s to destroy the main forts of the Maginot Line with their seven ton (800 mm caliber) shells from a distance of 29 miles (47 km)
Gustav was captured by American soldiers, but Dora was destroyed by the Wehrmacht in 1945 to avoid capture by the Red Army.
(via Indian Defence Forum and vintag.es)
The .600 Nitro Express Zeliska revolver, by the Austrian Pfeiffer Waffen, the largest handgun in the world, weighing 13.230 lb (6.001 kg), producing a muzzle energy of 7,591 foot pounds. It works with .600 Nitro Express cartridges, which were widely used for killing elephants in the early 20th century.
(via Vince Lewis)
Project Babylon, a supergun project of Saddam Hussein, began in 1988, but halted two years later, when the produced sections were seized in transit, and the Iraqi parts were destroyed by the UN in 1991.
Two Big Babylons would have 512 ft (156 m) long barrels, and weigh about 2,100 tonnes each, intended to shoot projectiles into orbit.
(Above: Two sections bolted together at Royal Armouries, Fort Nelson, Portsmouth, England, via Wikimedia Commons)
Panzerkampfwagen VIII Maus (Mouse), the heaviest fully enclosed armoured vehicle ever built. The 33 ft 6 in (10.2 m) long and 12 ft 2 in (3.71 m) wide super-heavy tank weighs 188 tonnes. (207 short tons) Only one prototype was complete.
It could go 45 ft (13 m) under water with a large snorkel. It was the only method to cross a river, because bridges were too weak to hold the Maus.
(via Wikimedia Commons and Tankpedia)