In early missions over France and the Low Countries there was no clear outcome regarding the success of the bombers’ guns: the Luftwaffe lacked widespread radar so their interception efforts were disorganised.

On 18 December 1939 a raid by three squadrons of Vickers Wellington against ships in the Heligoland Bight was detected on an experimental Freya radar long before it reached the target area.

The Germans had also studied this problem and had invested considerable effort in radio navigation techniques to address it, demonstrating a standard of bombing accuracy during the night raids that daylight forces found difficult.

The RAF lacked similar navigation systems, having ignored their development for a number of years and relied almost entirely on dead reckoning and optical instruments such as the Course Setting Bomb Sight.

Accepting the recommendations of Lindemann's report after intense debate, the British began planning a major offensive starting in the spring of 1942 with the aim of destroying German cities.

An obvious solution to Bomber Command's problems would be simply to copy the German technique of placing all available sets in a lead force.

In rebuttal, Sir Henry Tizard, adviser and one of the chief scientists supporting the war effort, responded, "I do not think the formation of a first XV at rugby union makes little boys play any less enthusiastically.”[3] Studying the German results, notably reports by R. V. Jones, the Air Ministry decided that the technique was sound and they overrode Harris' objections and forced the issue.

Harris responded by suggesting the pathfinders be distributed among the squadrons but again his objections were overruled, since it would not produce the desired result of having the targets clearly marked in advance of the arrival of the main force.

The group once again had great difficulty identifying its target in cloudy conditions and most of the bombs fell in open country north and west of the city.

Photographs showed that these were placed with great accuracy and the crews of the Main Force claimed to have carried out a good attack.

[9] On 1/2 September 1942 the PFF illuminated Saarbrücken as part of a 231-aircraft force, but post-raid analysis showed this to be Saarlouis, 13 miles to the north and situated on a similar bend in the river.

The next night a force of 200 bombers was led by accurate marking in Karlsruhe, and the raid was considered a great success, with an estimated 200 fires seen burning.

This led to the problem of "creepback", when the newly arriving bombers would drop their bombs on the near side of the fire so they could turn for home earlier.

The 'illuminators' would drop white target illuminators at points along the attack vector, allowing aircraft to follow these markers over long distances and thus avoid getting lost en route.

Added to this list were hundreds of light and medium industrial buildings, including the Weser aircraft works and the Atlas shipyard and associated warehouses.

[11] On the night of 15/16 October 1942 on a raid by 289 aircraft against Cologne, the Germans lit a decoy target indicator that deceived the majority of the Main Force's bombs.

On 20/21 December 1942 H. E. Bufton personally led a force of six de Havilland Mosquitos on a raid against a power station at Lutterade, a small town in the Netherlands.

A follow-up under more realistic conditions was carried out on the night of 31 December 1942/1 January 1943 against Düsseldorf, with two Mosquitos leading a force of eight Lancasters.

Another mission by three Mosquitos attacked the German night-fighter control room at Florennes airfield in Belgium, but there was complete cloud cover and the results were not known.

[citation needed] By January the pace of Bomber Command missions had dramatically increased, with major raids being carried out almost every night.

On 11/12 February 1943 against Wilhelmshaven, the PFF used their H2S radar for the first time, dropping parachute flares above the heavy cloud cover in a technique known as ‘sky marking’.

[citation needed] On the night of 20/21 June 1943 another change in technique was tested by 60 Lancasters (mostly from 5 Group) against Zeppelin works at Friedrichshafen, which were believed to be making radar.

[13] The follow-up force consisted of several groups, including PFF aircraft, who marked the target based on radio instructions from what would become known as ‘the Master Bomber’.

Another group of aircraft were to attempt a new technique, bombing at a specific time after passing a ground feature, in this case the shores of Lake Constance.

A combination of these techniques was first used on a large raid to great success on the night of 17/18 August 1943 in Operation Hydra against German rocket research at Peenemünde.

The estimate has appeared in many sources that this raid set back the V-2 experimental programme by at least two months and reduced the scale of the eventual rocket attack.

PFF crews found themselves given ever increasingly sophisticated and complex jobs that were constantly modified and developed tactically during the bombing campaign from 1943 until the end of the war.

Further "Markers" called "Backers-Up" or "Supporters" would be distributed at points within the main bomber stream to remark or reinforce the original TIs as required.

These were known by the codenames Parramatta, Wanganui and Newhaven – the names coming from locations in Australia, New Zealand and the UK which had links with Pathfinder staff.

[21] In all cases, further target Indicators would be dropped in the course of the raid to reinforce the marking and to compensate for earlier TIs either burning out or being extinguished by the bombing.