to describe all of the instruments in detail, but one type of equipment you may see, and will certainly recognize if you do, is the camera. Several kinds are employed to photograph the explosion, including one which takes pictures at the rate of 200,000 per second. Much of the equipment used is very complicated but some of it is very. simple. For example, the common tooth-paste tube is one of the things used to measure blast pressure.
      The SERVICES GROUPS have a number of commitments. There is the Headquarters (responsible for the directions and planning of the scientific element of the operation and for liaison with the Task Force), the head of this being the Scientific Director of the Operation, Mr. W. R. J. Cook, C. B., Deputy Director, Atomic Weapons Research Establishment. There are other Groups concerned with administration and provision of technical and scientific services, with the various aspects of health safety of personnel, with the prediction of the fall out of radioactive particles, protection against radioactivity and with decontamination. An Organization tree of the Scientific Party is shown overleaf.
      Before the final flight when the weapon is dropped several rehearsals must be held to make sure that every person knows his job, that the equipment on the ground, and in the ships and aircraft works correctly and that the timing for the operation is perfect. It is not only the scientists who must be absolutely sure of their part before the weapon is dropped but also you who are taking part in the Operation. This is an occasion for. team-work and perfection.
      First there are Flyover Trials. During these the bomber takes off from Christmas Island and flies to the target area where it carries out similar manoeuvres to those it will perform on D-Day. The aircraft carries a dummy weapon and some radio and electronic equipment. On the ground the Weapon, Measurements and Electronic Services Groups check the transmissions from the aircraft. The aircraft then returns to base and the results of the Flyover Trial are examined by the Weapon Groups. Any deficiencies in the equipment, either in the aircraft or on the ground or in the ship from 'which the scientific part of the operation is controlled, are put right and if necessary another Trial is held.
      After satisfactory completion of the Flyover Trials practice weapons are dropped. Once again the Weapon Groups and some scientists of the Measurements Groups test their equipment.
      Then comes the Operational Rehearsal. This is when all personnel and ships take up the positions they will occupy when the live drop takes place, and when all equipment is finally checked. The Weapon Groups carry out the procedure of assembling and loading the bomb into the aircraft with, of course, the Royal Air Force playing their part; the aircraft crew rehearse the ground checks and then take off; During this period, in the target zone and in the ships, scientists and members of the Services make final adjustments to their equipment and then take up their operational positions in the Naval ships which move out to their allotted station. All this takes place to a carefully laid-down time-table with everyone being checked to see that they are in the right place at the right time. The aircraft arrives over the target area, the last practice weapon is