[Canadian Army]

The UK Royal Navy's Fleet Air Arm used the Fairey Swordfish, a biplane design commissioned in 1936. It would have been helpless against enemy fighters (like most of the war's torpedo bombers), but it had an advantage against enemy AA: WWII rangefinders couldn't predict the flight path of anything that slow. Thus, attacks by Swordfish sank much of the Italian Navy in its home port of Taranto, and crippled the Bismark in its breakout attempt in the North Sea, both times with negligible British losses.

Nazi Germany assumed, at the beginning of the war, that horse cavalry were obsolete, but by 1942, they'd changed their minds. Infantry were too slow to catch Cossacks and mounted partisans, and tanks couldn't enter rocky ground and forests (which cavalry certainly could); the result was about ten divisions of German cavalry.

During the early stages of World War II, the Norwegians sank the heavy cruiser Blücher with weaponry which they'd bought decades before, and which was obsolete even then. The Norwegian commander wasn't sure that his fifty-year-old torpedoes would even work. They did.

Some Taliban snipers in Afghanistan use British Lee-Enfield rifles (or locally manufactured copies), which were designed in the 1880s and used in both World Wars. (A basically similar weapon chambered for NATO-standard battle rifle ammunition was in use by the British Army in the same role until relatively recently.) Their Iraqi counterparts prefer its Nazi rival, the Mauser Kar.98k (designed in 1935, as a cut-down version of the Mauser Karabiner model 1898).

In the Falklands War, the British took a WWII field kitchen truck from the Imperial War Museum and sent it along with the Task Force sent to fight off the Argentines, since there was no modern equivalent that could prepare hot meals in the field. This relic field kitchen even managed to land on East Falkland — which Argentina had already evacuated — before the Parachute Regiment, who had been tasked with retaking it.

Before they had their own defense industry (i.e., the Yom Kippur War and all previous conflicts), the Israelis relied on upgraded, surplus tanks. In the Yom Kippur War, they defeated state-of-the-art T-55s with heavily upgraded Shermans — proving that in the right hands and with the right modifications, even a thirty-year-old design that was never any good in the first place can defeat state-of-the-art technology.

During the Cold War, a squad of of SAS commandos were tasked with defending an Omani fort when they were suddenly attacked by hundreds of Communist guerrillas. In desperation, a couple of the SAS soldiers rushed over to a nearby shed that housed an antique WWII era anti-tank gun. They managed to get it working and it proved to be the deciding factor in the fight, buying them enough time for reinforcements to arrive.

During the Soviet war in Afghanistan, the mujahidin found that Stingers were not very useful (despite a few early successes), and preferred to fight Hinds with WWII AA guns.

The standard weapon issued to the Canadian Rangers (the militia force based in the Arctic) is the Mk 4 Lee-Enfield, first produced in 1939 and out of service with the regular Canadian military since the 1950s. The rifles are being replaced beginning in 2015...with another bolt-action rifle. The only reason the Mk4 is being replaced at all is that spare parts are running out.

The Soviet Union kept using vacuum tubes in its bombers long after the development of transistors, since vacuum tubes are resistant to EMPs and many kinds of electronic counter-measures (ECM).

During the initial stages of the Israeli War of Independance in '48, the Israeli supply situation was so bad that they even used Napoleonic-era, muzzle-loading cannons.

Blackburn Buccaneer a.k.a The Banana Jet. It was designed in 1954, and outlasted its all intended successors in both FAA and RAF use. It was finally withdrawn in 1994, because the airframes were too stressed to keep flying safely.

In the Korean War, North Korea used sea mines dating back to the Russo-Japanese War. (In fact, they're still using them.)

Most of the North Korean military carries equipment dating back to the 1970s or earlier. The forces deployed to defend the capital have more recent gear, but that's about it. Reportedly, some of their reservists don't even have firearms, and carry bladed weapons.

In 1807 the Ottomans loaded some giant cannons that had been collecting dust since the fall of Constantinople almost four centuries earlier and used them to repel a British attack on the Dardanelles. It worked.

The four Iowa-class battleships have been mothballed, and recommissioned, twice. And Congress wouldn't let the navy get rid of them completely, until the early years of the 21st century. All four are now gone, but are now literal museum pieces, as they have been made into floating museums (the Iowa in Los Angeles, the New Jersey in Camden, New Jersey, the Missouri in Pearl Harbor, Hawaii, and the Wisconsin in Norfolk, Virginia). After the release of Battleship, Slate ran an article positing whether or not it would be possible to return the Iowa-class battleships to active duty now that they're museum ships. It would actually be very easy, assuming that enough crew, fuel, and ammunition for its main guns are on hand for that.

The Korean People's Air Force has a small number of relatively modern fighter jets, including the MiG-29. They also operate many older airplanes. Including around thirty MiG-15s, as in the fighter jet they flew in the Korean War, although their remaining MiG-15s are all trainers.

The Antonov An-2 Colt transport, the smaller Russian cousin to the equally universal DC-3; is hard to pick up on radar, is so slow that modern fighters have trouble engaging it with guns, and it can take off and land from improvised air strips, making it an ideal commando or officer transport. For the same reasons, around ten are also used by the South Korean Air Force. Outside of the two Koreas, even smaller European countries like Estonia, Moldova and Macedonia also operate the An-2 as a paratrooper plane. And while fighting the Serbs in the early 1990s, Croatians even used them as improvised bombers to take out Serbian armoured vehicles and fortifications. While one or two were shot down, the plan worked.

Suggested but averted by Benjamin Franklin during the American Revolution. The Battle of Bunker Hill ended with them being driven off when they ran out of ammunition. Franklin suggested that if they had used bows and arrows, they could have held out longer and fired off volleys more rapidly. It may be possible that this referred more to the fact that at the start of the Revolution, the colonists were desperately short of gunpowder. At one point, there were literally only a few dozen barrels left for the entire army, which would have been just enough for one pitched battle without artillery. The situation did improve later on, when France became heavily involved in the war and started sending over regular supplies of the stuff.

English officers had been proposing this on and off throughout the 18th century. Trained longbowmen couldn't be beaten for sheer volume of fire until the introduction of breach-loading mechanisms and metallic cartridges; the catch is the "trained" part.

The first operational SR-71 was retired to the National Museum of the United States Air Force in the 70's, only to be put back into service for 20 years and permanently retired in 1990. But perhaps the retirement was premature, since the plane broke an air speed record on the way to the museum.

When British firefighters went on strike in 2002, the Army was called upon to provide cover. They made extensive used of "Green Goddess" fire engines, built in the 50s and mothballed in the late 60s. The law has now been changed so in a future strike, the Army would have access to the fire brigade's equipment, and the Green Goddesses have been sold to developing countries.

The Italian Air Force used the F-104 until 2004 in spite not only of the extreme age of the design (the airplane was first flown in 1954, with the Italian F-104S version being manufactured between 1964 and 1979) but of its tendency to crash. It helped it was actually faster than the more modern F-16 that had been considered to replace it in the 1980s...

During Homeland War, some Croatian units used M4 Sherman tanks and US WWII M36 Jackson tank destroyers. They proved effective in infantry support.

Some navies keep old 7.62mm chambered rifles on board in addition to standard 5.56mm for resupply at sea evolutions. The reason? The 5.56mm blank cartridges are unable to propel the line far enough to reach the other ship.

The Finnish Army Field Kitchen, m/29 Soppatykki (Soup Cannon). Originally designed in 1929 for horse-drawn troops and be used with firewood, it is still in production, adapted to be towed by lorries and smaller motor vehicles. The redesign, m/85, is merely an incorporation and documentation of all changes and improvements on the original. Several of the WWII veteran field kitchens are still in use.