Belgium, Canada, Denmark, France, Germany, Greece, Italy, Netherlands, Norway, Portugal, Spain, Turkey, United Kingdom and the United States.

Here BBC News Online gives you details of the key items of military hardware being used in Kosovo.

Click here for Nato - air , land , and sea forces.

Click here for Yugoslav - air and air defence forces.

Depending on which of the air or phased air options is implemented, the operation requires up to 400 aircraft.

As of 21 February 1999, over 300 were committed to this operation and many of them are already deployed forward on stand-by at various air bases in Italy and other Nato nations or on carrier vessels.

Nato forces - AIR

The F-16 is Nato stalwart

F-16 Fighting Falcon - This aircraft is the most important weapon in Nato's arsenal. Built by an unusual consortium of the USA and four Nato countries, it is the closest thing Nato has to a standard fighter.

As well as excellent manoeuvrability and speed, it is proven in air-to-air and air-to-ground combat, with a speciality of being a 'harm-shooter', meaning it can take out radar systems.

The F-16 is a compact, multi-role fighter aircraft. The F-16A, a single-seat model, first flew in December 1976. The first operational F-16A was delivered in January 1979 to the 388th Tactical Fighter Wing at Hill Air Force Base, Utah.

USAF F-16 multi-mission fighters were deployed to the Persian Gulf in 1991 in support of Operation Desert Storm, where more sorties were flown than with any other aircraft. These fighters were used to attack airfields, military production facilities, Scud missiles sites and a variety of other targets.

Contributing countries: Belgium, Denmark, Netherlands, Portugal, Turkey, Norway, USA

The B-52 can carry 20 cruise missiles

B-52 Stratofortress - Eight US B-52 bombers out of 15 are operating out of RAF Fairford, Gloucestershire, England - armed with up to 20 cruise missiles.

They are capable of dropping 30 tons of bombs. Three B-52s can leave a crater, a mile square and 50ft deep. They can fly for 7,000 miles without refuelling and their penetrator bombs can destroy a building 1,000ft away.

Contributing country: USA

The B-2 avoids detection

B-2 Stealth bomber - America's "bat plane" has recently also been called the 'ace in the hole' of the US aviation armoury.

The world's most costly plane at �812m, it can fly without aerial refuelling from the US to Serbia and back.

It is designed to be able to evade enemy radar and has 40,000lb of bombs including new "smart" bombs, among them the "bunker-busting" GBU-28.

The US claims it is completely invisible to radar.

Contributing country: USA

The airborne early warning aircraft are the lynch-pin of the integrated military force

E-3A (D) Airborne Early Warning - This aircraft is the 'eyes in the sky' of the Nato force. It provides a high-altitude communications base monitoring the action on the ground - of both sides.

It is the lynch-pin of Nato's integrated defence system and is the mastermind that should give Nato forces the advantage over Yugoslav commanders.

The E-3 Sentry is a Boeing 707-320B airframe packed with radar and electronic sensors. Easily distinguishable by the large rotodome mounted above the rear fuselage, the Sentry is an Airborne Early Warning (AEW) platform which carries a flight crew of four and 13 or more systems operators.

Cruising at 29,000 feet, the E3's capability significantly extends the range of ground based radars, giving longer warning time of the approach of potentially hostile targets.

Contributing countries: USA, UK

The UK's Harriers will take on some of the most dangerous missions

Harrier GR-7 - 8 x Harrier GR7s of 3(F) Squadron based at Gioia del Colle, Italy.

The world's oldest air squadron is spearheading Britain's contribution to the multi-national air armada in Italy.

Pilots and groundcrew from the RAF's No 1 Fighter Squadron are flying eight Harrier GR7 ground attack aircraft the latest generation of the jump-jet.

The fighter-bombers are able to take-off or land vertically and are fitted with infra-red equipment.

They carry 1,100lb and 2,000lb bombs and are armed with sidewinder missiles

Having proved itself in Bosnia, Nato knows the plane is suited to the terrain. But it is also a versatile and highly effective fighter/bomber.

The Harriers are equipped with the most up to date night vision systems, making the GR7 day/night capable.

They carry awesome firepower including up to 16 Mk 82 or six Mk 83 bombs, six cluster bombs, four Maverick ASMs, or 10 rocket pods on seven wing stations.

It also uses the same precision guided weapons systems that Tornadoes have been using in Iraq - and which have been attaining an impressive direct hit rate of 80%.

The Tristar is used for transport and in-air refuelling

L-1011 Tristar - Tristar tanker/transport support based at Ancona, Italy.

The RAF operates a number of Tristar aircraft in the transport role. The Tristar C2s are dedicated transport aircraft and can carry 265 passengers and 16 tonnes (35,000 lbs) of freight over ranges in excess of 4,000 miles.

The other two variants, the K1 and the KC1, are dual role and capable of providing air-to-air refuelling from a pair of centerline fuselage hoses. The K1 can carry 204 passengers; however, the KC1 has a large freight door and can carry 20 cargo pallets, 196 passengers or a combination of mixed freight and passengers. The VC10 and Tristar fleets are based at RAF Brize Norton in Oxfordshire.

LAND

NATO's ground troops are currently stationed in the former Yugoslav republic of Macedonia.

There are 4,800 UK soldiers among 10,000 NATO troops. Defensive measures are being taken as Macedonia-based troops are seen as being the most vulnerable to attack. They are within range of Yugoslav artillery.

The main British base is at Veles, but there are units near Skopje and Kumanovo close to the Kosovo border. Unconfirmed reports say that SAS special forces are in the area.

SEA

HMS Splendid fired the Royal Navy's first Tomahawk cruise missile in anger during the first wave

The British nuclear-powered submarine, HMS Splendid, stationed in the Adriatic has fired Britain's first cruise missile in anger at Yugoslavia.

It is the first British submarine able to launch the missiles which can travel at 550mph and hit targets hundreds of miles away.

Splendid: Displacement: 5,000 tonnes Length: 82.9m Beam: 10.1m Complement: 116 Armament: Harpoon anti-shipping missiles, Spearfish torpedos, Tomahawk Land Attack cruise missiles

YUGOSLAV FORCES

Overall Numbers

• Army strength: 85,000 soldiers and possibly 200,000 reservists
• Naval strength: 15,000
• Air Force strength: 15,000

AIR FORCES

MiG-29 Fulcrum - A relatively modern Russian fighter. The most modern aircraft in the Yugoslav inventory, though the air force has only about a dozen at most.

MiG-21 Fishbed - A 1960s designed air defence fighter. This model is still capable but is old. The Yugoslav Air Force has about 70.

AIR DEFENCE

Strategic Systems - SA-2, 3 and SA-6 surface-to-air missiles (SAMs).

The first two are old and not a worry to Nato forces. But the latter is a very effective medium level missile which, although it is well known, is also to be feared and given due respect.

It has already been used in anger in Bosnia and was the weapon responsible for shooting down USAF Capt Scott O'Grady's F-16 in 1995.

Tactical Systems - SA-9 and 13. Essentially the same missile; the first is mounted on a wheeled chassis, the second on a tracked chassis.