From Air 27 1067 Public Records Office, Kew

The method used to drop the mines in the desired position is to select a prominent datum, such as one bank of a river mouth, headland etc, and to set course from there on a given track, height and ground speed, and to drop the mines by timing from a stop watch.

This procedure is shared by three people:

Captain: is responsible for course and height.

2nd Pilot: is responsible for speed by necessary manipulation of the throttles.

Navigator: is responsible for the timing and actual release of the mines.

Where possible it is advisable to do the dropping on 'George' for two reasons: -

(i) Accuracy in piloting.

(ii) Search lights have a blinding effect and when caught in same there is a great tendency to push the stick forward. If flying on 'George' you are safe for a few seconds by which time you can readjust as necessary.

Undoubtedly our greatest difficulty has been the inaccuracy of maps and charts for almost every port, harbour or area we have mined. Photographs, when available, are invaluable and it is strongly recommended that P.R. cover be obtained of the area concerned before mining operations are attempted. This Squadron has had several abortive sorties due to rivers, inlets etc not existing, or existing in places not indicated on maps or charts.

The usual is as follows:-

Height: 350 feet.

Speed: Ground Speed of 175 M.P.H.

In the event of the presence of flak ships it is advisable to use a dropping height of 200 feet to reduce the flak risk.

Sometimes the last wind found is used for working out course and indicated speed for the run, but owing to the variation of wind around coastlines, it is more accurate to use a visual wind found within a few miles of the target area. Naturally this is not always possible.

Information Required

(1) Number of aircraft to be employed.

(ii) Number, type and assemblies of mines to be used.

(iii) Admiralty charts of area to be mined.

(iv) Latest detailed information of coastline within twenty miles radius of target - photographs where possible.

(v) Latest information on defenses, especially L.A.A. and searchlights.

(vi) Information on enemy Radar cover to and from target and in target area.

(vii) Any information on much used channels, swept channels etc, this is rarely if ever, supplied but much information can be gleaned from Coastal Pilots.

The charts, maps and photographs are then perused for suitable datums, and a pattern is then designed to close all inner entrances and, when sufficient A/C are available, to lay an outer pattern as a sort of second line.

During the laying on of a sortie, great care is taken to ensure that aircraft's tracks do not cross during their dropping run or on their run ups to their datums: if they do, aircraft are given different heights to fly.

After last mine away aircraft are given "break aways" care again being taken t ensure that tracks do not cross of that height bands are given. Usual procedure is to remain at minimum altitude 50-100 feet until at least 50 miles from target area.

Aircraft are given height bands of 1,000, 800, or 1,200 feet to fly on their way out but whenever within Radar cover they descend to a sufficiently low height to guarantee evasion. Out of Radar cover on the return trip aircraft are given heights bands between 7,000 and 10,000 feet i.e. at the best height for range flying in a Liberator of that weight.

To ensure equal spacing of aircraft in the target area, the number of 3 course winds to e bound on the way out is laid down before take off according to the Met. Forecast. This point is at the Captains discretion for the return trip.

When approaching the target it is highly desirable to "aim Off" by about 10-20 miles for the landfall, and then to come down the coastline to the datum. Although this takes a little longer it ensures that when you're in the target or danger area, you know exactly where you are and what you are going to do next, with the result that the absolute minimum of time is spent in the target area.

The approach to the target is made at a height of between 600-1,200 feet to facilitate map reading, and once the datum is identified, height is lost down to the dropping height, and speed set at dropping speed.

In this squadron the navigator passes the dropping speed and course to the captain about 5 minute before reaching the target. The navigator also opens the bomb doors, selects bays and fuses mines about 1 minute before reaching the datum, repeating same to the captain over intercom as he does so.

Normal spacing between take offs is three minutes - this prevents over crowding in the target area. However, if a large number of aircraft is to be employed on a rugged target, owing to the undesirability of lingering in the target area the take off interval is reduced to 1 minute.

This Squadron is equipped with Mk. V. Radar and it has proved invaluable. A great deal of time has been spent in training one Radar Operator i each crew in map reading by radar, and the results achieved have exceeded all expectations. Ranges of 90 miles and over on mountains when the aircraft is flying at 500 feet and below are the rule and not the exception. I conditions of low visibility the air craft have many times been guided to their datum by radar alone, and in a few instances the complete run has been carried out and mines dropped successfully entirely o radar - the datum not being sighted visually at all.

Another great use of this equipment in the hands of a good operator is to combat bad weather. In tropical regions CU. and CUNG. Clouds are such great vertical structure that they may threaten structural damage to aircraft. On a dark night it is impossible to pick your way visually through these clouds, but by using the radar it is possible to plan your flight 30 or 40 miles ahead so as to avoid any cloud which may be hasardous to the aircraft.

Finally, radar has been used to pick up enemy night fighters at ranges of 5-10 miles and the resultant avoiding action has, so far, been entirely successful.

All this Squadron's aircraft are fitted with radio altimeters, 0-400 feet, and these are considered an essential fitting for aircraft engaged on low level mining operations.

Once the sorties have been planned Form's Green are produced for individual aircraft giving full details of heights to fly, tracks, approach to datum, break aways etc.

For the briefing, all crew members are mustered in the Ops. Room and are addressed by the following people in the following order on the matters listed against their names.

1. Intelligence Officer.

Location of target, reasons for importance, Local Defenses: - includes H.A.A. L.A.A. searchlights, Aerodromes and aircraft. Local pick up points. Maps and photographs of aircraft datums.

2. Met. Officer.

General weather to and from target and weather in target area.

3. Signals Officer.

Normal signals briefing.

4. Squadron Commander or Flight Commander.

General considerations, tactics to be employed on these particular sorties. A detailed run over each aircraft's sortie.

5. Ops. Officer

Normal G.R. briefing as applicable. Air Sea rescue facilities available, including dispositions of our submarines in target area and on track to and from target.