Biggest planes ever built (unfinished)

War History Online has an article (go there for the photos) about some really big airplanes:

Bigger is better has certainly been true in military aviation history. Spurred on by the First and Second World Wars, ever-bigger airplanes were designed and developed, culminating in the truly gigantic H4 Hercules which flew, if only a bit, in 1947. When looking at wingspan, it is yet to be superseded.
We have selected ten that were built over the past 75 years: 

Junkers JU 390 The Junker JU 390 was designed by the Nazis in 1942, intended to be as a heavy transport, maritime patrol aircraft, and long-range bomber, a long-range derivative of the Ju 290. It was one of the aircraft designs submitted for the abortive Amerika Bomber project.
Only two were ever completed; their maiden flight was in October of 1943 and, although 26 were ordered, it never went into production. The orders were cancelled in June of 1944. With the end of the Third Reich, this plane faded out of aviation history.
The plane was just over 112 feet long and had a wingspan of 165 feet and had a range of around 6000 miles. 

Antonov AN-225 The Antonov An-225 Mriya was designed by the then-Soviet Union’s Antonov Design Bureau in the 1980s. It is powered by six turbofan engines and is the longest and heaviest airplane ever built, with a maximum takeoff weight of 640 tons. It also has the largest wingspan of any aircraft in operational service.
The Antonov An-225, initially developed for the task of transporting the Buran spaceplane, was an enlargement of the successful Antonov An-124. The first and only An-225 was completed in 1988. After successfully fulfilling its Soviet military missions, it was mothballed for eight years. It was then refurbished and re-introduced, and is in commercial operation with Antonov Airlines, carrying oversized payloads.
The enormous plane is 275 feet long and has a wingspan of 290 feet. 

Messerschmitt ME 323 The Messerschmitt Me 323 was a German military transport aircraft of World War Two. It was a powered variant of the Me 321 military glider and was the largest land-based transport aircraft of the war. A total of 213 are recorded as having been made.
The Me 323 was the result of a 1940 German requirement for a large assault glider in preparation for the projected invasion of Great Britain. After that operation was scrapped, the need remained for a heavy transport that could deliver vehicles and supplies. The ME 321, the glider version, was produced first and, in 1941, the decision was taken to produce a motorized variant, to be designated Me 323.
The maximum payload was around twelve tons, but it was a very slow aircraft, having a top speed of only 177 MPH. It was just over ninety feet long and had a wingspan of over 181 feet. None of the ME-323s survived the war. 

Blohm & Voss BV 238 The Blohm & Voss BV 238 was a German flying boat built during World War Two. It was the heaviest aircraft ever flown when it first flew in 1944, and was the largest aircraft produced by any of the Axis powers.
The sole completed BV 238 was strafed and sunk while docked on Schaalsee, the RAF having discovered it in late April of 1945. The ˆ were reportedly concerned that Adolf ˆ could use it to escape to South America, and so an attack followed shortly after its discovery. The aircraft was attacked by Hawker Typhoons or Tempests. Their strafing set the engines alight, and the aircraft burnt and sank with only part of a wing remaining above the surface. Production of two other prototypes was begun but neither was finished. This flying boat was 142 feet long and had a wingspan of 197 feet. 

Martin JRM Mars The Martin JRM Mars is a large, four-engined cargo transport seaplane originally designed and built in limited numbers for the Navy during World War Two. It was the largest flying boat to enter production, although only seven were built. The Navy contracted the development of the Mars in 1938 as a long range ocean patrol flying boat, which later entered production as the Martin JRM Mars long range transport.
The surviving aircraft were later converted for civilian use to firefighting water bombers. One example of the aircraft still remains in active service. It is over a hundred feet long and has a wingspan of two hundred feet.

Convair B-36 “Peacemaker” The Convair B-36 “Peacemaker” was a strategic bomber and operated solely by the Air Force from 1949 to 1959. The aircraft was unveiled on 20 August 1945, and flew for the first time on 8 August 1946. The B-36 was the largest mass-produced piston engine aircraft ever made. It had the longest wingspan of any combat aircraft ever built, at 230 feet. The B-36 was the first bomber capable of delivering any of the nuclear weapons in the US arsenal from inside its four bomb bays without aircraft modifications.
With a range of ten thousand miles and a maximum payload of 72,000 pounds, the B-36 was the world’s first manned bomber with an un-refueled intercontinental range. 

Convair XC-99 The Convair XC-99 was a prototype heavy cargo aircraft. It was the largest piston-engined land-based transport aircraft ever built, and was developed from the Convair B-36 bomber, sharing the wings and some other structures. The first flight was on 24 November 1947 in San Diego, California and, after testing ,it was delivered to the Air Force on 26 May 1949. The Convair Model 37 was a planned civil passenger variant based on the XC-99, but was not built.
In July of 1950, the XC-99 flew its first cargo mission, Operation Elephant, but, after a few missions the Air Force determined that it had no need for such a large, long-range transport at that time, and no more were ordered. The sole XC-99 served until 1957, including use during the Korean War. Its last flight was on 19 March 1957, landing at Kelly Air Force Base, where it would remain for the next 47 years.
It is currently disassembled and in storage in Arizona with no plans to restore it in the foreseeable future. When still assembled, it had a length of 182 feet and a wingspan of 230 feet. 

Boeing B-52 In a conventional conflict, the B-52 can perform air interdiction, offensive counter-air, and maritime operations. During Desert Storm, B-52s delivered forty percent of all the weapons dropped by coalition forces. It is highly effective when used for ocean surveillance, and can assist the Navy in anti-ship and mine-laying. Two B-52s, in two hours, can monitor over a hundred thousand square miles of ocean. All B-52s are equipped with an electro-optical viewing system that uses platinum silicide forward-looking infrared and high resolution low-light-level television sensors to augment the targeting, battle assessment, flight safety, and terrain-avoidance system, thus further improving its combat ability and low-level flight capability.
Beginning with the successful contract bid in June of 1946, the B-52 design evolved from a straight wing aircraft powered by six turboprop engines to the final prototype YB-52 with eight turbojet engines and swept wings. The B-52 took its maiden flight in April of 1952. Built to carry nuclear weapons for Cold War-era deterrence missions, the B-52 Stratofortress replaced the Convair B-36. A veteran of several wars, the B-52 has dropped only conventional munitions in combat.
The B-52 has been in active service with the USAF since 1955. As of 2012, 85 were in active service, with nine in reserve. The B-52 completed fifty years of continuous service with its original operator in 2005; after being upgraded between 2013 and 2015, it is expected to serve into the 2040s. It has a length of 159 feet and a wingspan of 185 feet.

Hughes H-4 Hercules The Hughes H-4 Hercules is a prototype heavy strategic airlift military transport aircraft. Intended as a transatlantic flight transport for use during World War Two, it was not completed in time to be used in the war. The aircraft made only one brief flight on 2 November 1947, and the project never advanced beyond the single example produced.
Built from wood because of wartime restrictions on the use of aluminium and concerns about weight, it was nicknamed by critics the Spruce Goose, although it was made almost entirely of birch. The Hercules is the largest flying boat ever built and has the largest wingspan of any aircraft in history.
It is on display, and remains in good condition at the Evergreen Aviation & Space Museum in McMinnville, Oregon. The length of the Hercules is 218 feet and an incredible wingspan of 320 feet 

Lockheed C-5 Galaxy The Lockheed C-5 Galaxy provides the Air Force with a heavy intercontinental-range strategic airlift capability, one that can carry massive loads. The C-5 Galaxy has been operated by the USAF since 1969. In that time, it has been used to support US military operations in all major conflicts including Vietnam, Iraq, Yugoslavia, and Afghanistan; as well as in support of allies, such as Israel during the Yom Kippur War and operations in the Gulf War. The C-5 has also been used to distribute humanitarian aid and disaster relief, and supported the Space Shuttle program run by NASA. The airplane is 247 feet long with a wingspan of just over 229 feet, and can carry a staggering two hundred tons of cargo.

Rico says them's some big-ass airplanes...