'Crossbow' was the British and US operation against the German long-range reprisal weapons (V-weapons) programme (15 November 1943/13 April 1945).

The main V-weapons were the V-1 flying bomb and V-2 ballistic missile that were launched against European mainland and British targets in 1944/45.

Initial intelligence investigations of 1943 into the progress of German long-range weapons capability were carried out as 'Bodyline', and on 15 November a more substantial operation was inaugurated as 'Crossbow'. This latter included strategic operations against the research and developments of these weapons, their manufacture, transportation and launch sites, and fighter interceptions of missiles in flight. At one point, the British government was so concerned that it ordered that 40% or more of all bomber sorties be targeted against the launch sites. The 'Crossbow' attacks were in effect pointless, it has been argued, for every raid against a V-1 or V-2 launch site was one fewer raid against militarily and/or economically more important targets in Germany, and thus the diversion of Allied resources from other targets represented a major success for Adolf Hitler.

In May 1943 Allied reconnaissance detected the construction of the first of 11 large sites in north-eastern France for German secret weapons, including six for the V-2 missile. In November continued reconnaissance discovered the first of 96 so-called 'ski sites' for the V-1 flying bomb. The extent of the danger posed by the new German weapons was the subject of considerable debate: some viewed the sites as decoy undertakings designed to divert Allied bombers, while others feared that the weapons might be employed for the delivery of chemical and/or biological warheads. The Allies also received detailed information about the V-1 and V-2 missiles, and also the German development centre on Peenemünde island, just off Germany’s Baltic Sea coast, from the 'Cassia' Austrian resistance group headed by the priest Heinrich Maier. This also supplied information about production sites such as the Raxwerke outside Vienna. When the combination of reconnaissance and intelligence information regarding the V-2 became convincing, the British War Cabinet Defence Committee (Operations) directed the campaign’s first planned raid, which was schemed and implemented as the 'Hydra' attack on Peenemünde in August 1943.

The works in France were the 'Site System 1', which was to comprise 96 fixed launching sites with storage bunkers and outdoor ramps reminiscent of upward-tiled 'ski jumps'. 'Site System 2' was schemed as a reserve, and a 'Site System 3' were also planned. There were also four larger Wasserwerk (waterwork) bunker sites at Siracourt, Lottinghen, Nardouet and Brécourt. Intended for service from January 1944, the system was much delayed in construction, the training of the launch teams and the supply of V-1 missiles, all of which were found to be considerably behind schedule when inspected by German high command teams in October. Reports from agents and resistance elements in France combined with detailed photo-reconnaissance imagery associated with overflights of Peenemünde indicated the possibility that as many as 2,000 missiles per day might be planned as part of the German 'reprisal effort' against the UK, or more specifically the southern part of England. More than half of the sites had been completed by December, and Allied intelligence had identified all 96 by end of January. The first bombing of sites was by USAAF Martin B-26 Marauder medium bombers early in December, and Air Chief Marshal Sir Arthur Harris’s RAF Bomber Command began nocturnal attacks soon after this, but the greater inaccuracy of night bombing against small targets led Joint Chiefs-of-Staff to order the use of US heavy bombers in daylight. By end of December 54 sites had been attacked and seven destroyed. The bombing continued, and by end of March nine sites had been destroyed and 35 seriously damaged, and by May 24 sites had been destroyed and 58 significantly damaged.

Following 'Hydra', a few other 'Crossbow' attacks were undertaken against the 'Heavy Crossbow' bunkers of Watten (V-2) and Mimoyecques (V-3 'pump gun' long-range artillery weapon) from August and November 1943 respectively. 'Crossbow' operations against 'ski sites' began on 5 December: the codename 'Noball' was used for the targets ('Noball No. 27' was the Ailly le Vieux Clocher site, 'Noball No. 93' was in the area of Cherbourg. 'Noball No. 107' was at Grand Parc, and 'Noball No.147' was at Ligescourt.

The USA formed its own Crossbow Committee under the command of Major General Stephen G. Henry as the New Developments Division on 8 December 1943, and the US subsequently developed bombing techniques suitable for use against 'ski sites' in February and March 1944.

The 'Danny' plan developed in the middle of 1944 for US Marine Corps Vought F4U Corsair single-engined fighter-bombers operating from aircraft carriers and armed with 11.75-in (298-mm) 'Tiny Tim' heavyweight unguided rockets to attack V-1 launch sites fell victim to inter-service rivalry as it was opposed by the US Army. V-2 facilities were also bombed in 1944, including smaller facilities such as V-2 storage depots and liquid oxygen plants, such as the Mery sur Oise V-2 storage depot on 4 August 1944, and by Lieutenant General James H. Doolittle’s US 8^th Army Air Force on 25 August 1944, when five liquid oxygen plants in Belgium were attacked. A planned attack on the following day on plants at La Louvière, Torte and Willebroeck in Belgium had to be aborted as the facilities were covered by cloud.

At the request of the British War Cabinet, on 19 April 1944 General Dwight D. Eisenhower, the commander in chief of the Supreme Headquarters Allied Expeditionary Force, directed that 'Crossbow' attacks were to have absolute priority over all other air operations, including 'wearing down German industry' and hitting civilian morale 'for the time being', which he confirmed after the V-1 assault began on the night of 12/13 June 1944, saying to Air Chief Marshal Sir Arthur Tedder, his deputy, 'with respect to Crossbow targets, these targets are to take first priority over everything except the urgent requirements of the Overlord battle; this priority to obtain until we can be certain that we have definitely gotten the upper hand of this particular business'.

The start of the V-1 campaign surprised the Allies, who had believed that the earlier attacks on the sites had eliminated the danger. The British, who had not expected German attacks on the UK to be resumed so late in the war, were especially concerned. Some suggested using gas on the launch sites, or even executing German civilians as punishment.

Lieutenant General Carl A. Spaatz, commander of the US Strategic Air Forces in Europe, responded on 28 June to 'complain that Crossbow was a ''diversion'' from the main task of wearing down the Luftwaffe and bombing German industry' within the context of the 'Pointblank' combined bomber offensive, and to recommend instead that 'Crossbow' be a secondary priority since 'days of bad weather over Germany’s industrial targets would still allow enough weight of attack for the rocket sites and the lesser tactical crises'. By 10 July, Tedder had published a list of 'Crossbow' targets which assigned 30 to RAF Bomber Command, six to Air Marshal Sir Trafford Leigh-Mallory’s tactical Allied Expeditionary Air Force, and 68 to Spaatz’s USSTAF; after which Spaatz again complained,  so on 18 July Eisenhower permitted 'spare' bombing of non-'Crossbow' targets: 'Instructions for continuing to make Crossbow targets our first priority must stand, but…when…the entire strategic forces cannot be used against Crossbow, we should attack – (a) Aircraft industry, (b) Oil, (c) Ball bearing, (d) Vehicular production'.

More than 25% of the combined bomber offensive’s bomb tonnage were used against V-weapon sites in July and August: many of the attacks were ineffective as they were delivered against unused sites rather than the launchers themselves. Spaatz unsuccessfully proposed that attacks concentrate on the Calais electrical grid, and on gyro-compass factories in Germany and V-weapon storage depots in France. The gyro-compass attacks, along with the targeting of liquid oxygen tanks needed for the V-2 needed, might have been very effective against the missiles. On 25 August, 1944, the Joint Crossbow Target Priorities Committee, which had been created on 21 July, prepared the Plan for Attack on the German Rocket Organization When Rocket Attacks Commence: in addition to the bombing of storage, liquid oxygen production facilities and launch sites; the plan provided for air reconnaissance operations. After the final V-1 launch from France on 1 September, and since the expected V-2 attacks had not begun, 'Crossbow' bombing was suspended on 3 September and the campaign against German oil facilities became the highest priority.

The V-1 threat from occupied France ended on 5 September, when the Canadian 3^rd Division contained the German military units in the Nord Pas de Calais area, with their surrender following on 30 September.

The 'Crossbow' bombing effort was resumed after the first V-2 attack and included on 17 September a large raid on Dutch targets suspected as bases for Heinkel He 111 twin-engined bombers being operated as aerial launch platforms for the V-1. Some 865 modified V-1 weapons were air-launched from 16 September to 14 January 1945. The British had initially considered that an earlier effort of 18 July 1944, when of 50 V-1 weapons had been air-launched, to have been ground-launched from the Low Countries, particularly near Ostend. In addition to air-launched V-1 weapons, launches were from ramps built in the province of South Holland in the Netherlands during 1945. Allied air reconnaissance detected two sites at Vlaardingen and Ypenburg, along with a third at Delft. These launched 274 V-1 weapons at London on 3/29 March 1945: only 125 of them reached the British defences, and only 13 of those reached the target area. Three additional sites directed their fire on Antwerp. After using medium bombers against V-2 launch site in the Haagse Bos on 3 March, the RAF attacked the Dutch V-1 sites with two squadrons; One unit of Air Chief Marshal Sir Roderic Hill’s RAF Fighter Command used Supermarine Spitfire single-engined fighter-bombers against Ypenburg on 20 and 23 March, and one unit of Air Marshal Sir Arthur Coningham’s 2^nd Tactical Air Force used Hawker Typhoon fighter-bombers against Vlaardingen on 23 March. Counterattacks on Dutch V-1 and V-2 sites ended on 3 April, and all 'Crossbow' operations came to an end on 2 May as the war in Europe was almost over.

On 2 January 1944, the Air Defence of Great Britain command submitted a plan to deploy 1,332 anti-aircraft guns for the defence of London, Bristol and the Solent against the V-1 with a 'Diver' Operations Room at RAF Biggin Hill. Against V-1 attacks there were belts of select units of Fighter Command (No. 150 Wing) operating high-speed fighters, the anti-aircraft guns of General Sir Frederick Pile’s Anti-Aircraft Command, and about 1,750 barrage balloons of Air Marshal Sir Leslie Gossage’s (from 1 February 1944 Air Vice Marshal W. C. C. Gell’s) RAF Balloon Command around London.

'Flabby' was the codename for medium weather-conditions when fighters were allowed to chase flying bombs over the gun belt to the balloon line, and during 'Totter', Air Commodore F. Crerar’s Royal Observer Corps fired 'Snowflake' ground-launched illuminating rocket flares to identify V-1 flying bombs to RAF fighters. After the 'Robot Blitz' had begun on the night of 12/13 June 1944, the first RAF fighter interception of a V-1 took place on 14/15 June. Moreover, anti-aircraft guns increased the rate at which they downed V-1 missiles to one for every 77 rounds fired after the introduction of proximity-fused ammunition. Despite the defences, by 27 June 'over 100,000 houses had been damaged or destroyed by the V-1…and shattered sewage systems threatened serious epidemics unless fixed by winter'.

Of the 638 air-launched V-1 weapons that were observed, guns and fighters brought down 403: 66 fell in the London Civil Defence Region and 169 in other places, including Southampton on 7 July and one as far to the north-west as Manchester.

The British intelligence services (Secret Intelligence Service and the Air Ministry’s Scientific Intelligence Office) monitored German rocket artillery research and collated information derived from the bugging of higher-ranking German prisoners of war on an increasing basis, and this led to the steadily increasing focus on activities at Peenemünde. In response to discussions by the vice chiefs-of-staff on the subject of German long-range rocket developments, in April 1943 the politician Duncan Sandys was given responsibility for the investigation of how far Germany had progressed. Under the codename 'Bodyline', investigations by the SIS, the Combined Services Detailed Interrogation Centre and the RAF’s Photographic Reconnaissance Unit were able to confirm the existence of rocketry activities at Peenemünde, and Sandys reported his findings to the chiefs-of-staff that the Germans were developing rockets, were probably well-advanced and that the matter of countermeasures should be studied.

The 19-man Bodyline Scientific Committee was created in September 1943 to consider the suspected V-2 rocket. After the 1944 crash of a test V-2 in Sweden, 'transmitters to jam the guidance system of the rocket' were prepared. A British sound-ranging system provided 'trajectory [data] from which the general launching area could be determined', and microphones in East Kent reported the times of the first V-2 arrivals on 8 September 1944 as 18.40.52 and 18.41.08.

In November 1943, the Bodyline Scientific Committee transferred its tasks to the Air Ministry as the extent of the issue became clear.

On 21 March 1945, the Pile’s plan for the Engagement of Long Range Rockets with AA Gunfire, which called for anti-aircraft units to fire into a radar-predicted airspace to intercept the V-2, was ready, but the plan was not implemented as a result of the danger of shells falling on Greater London.

Unlike the V-1, which was comparable in speed with a fighter, the velocity and trajectory of the V-2 made aircraft interception an impossibility. Even so, there were cases of Allied aircraft encountering launched V-2 rockets: on 29 October 1944, for instance, Lieutenants Donald A. Schultz and Charles M. Crane in Lockheed P-38 Lightning twin-engined fighters attempted to photograph a launched V-2 above the trees near the Rhine river; on 1 January 1945, a pilot of the 4^th Fighter Group over the northern flight path for attacking elements of five German fighter wings in 'Bodenplatte' saw a V-2 'act up for firing near Lochem… the rocket was immediately tilted from 85 deg. to 30 deg'; and on 14 February 1945 the pilot of a No. 602 Squadron Spitfire F.Mk XVI fired at a V-2 just after it had been launched.

After the last combat V-2 launch on 27 March 1945, on 13 April the British discontinued the use of radar in the defence region to detect V-2 launches.