British Bomb, 250 lb TI, No. 17 Mk 1, Mk 3
The corresponding marks of the numbered bombs listed in this section are identical in construction and operation. They differ only in the types of candles they contain. Bombs Mk I and Mk II are nose-fuzed only, while Mks IC and III have provisions for both nose and tail fuzing.
Mk I Body - The Mk I bomb body consists of a heavy-gauge steel tube, to one end of which is welded a steel nose. The after end of the body is closed by a tail plate held in place by six brass rivets. The tail plate has two bayonet slots and a hole to be engaged by a transit base or the tail unit.
Immediately abaft the burster container is the ejection plate, slightly smaller than the internal diameter of the bomb body, to which the central flash tube is welded. The division disc, which separates the two layers of candles, is located at the opposite end of the flash tube. The inside of the tube and both sides of the division disc are covered with primed cambric. The igniter ends of both layers of candles rest against one of the primed discs.
The candles are held in position in the bomb body by felt or corrugated paper strips lining the inside of the body, a number of notched packing discs located beneath the tail plate, and a notched washer located against the ejection plate. Three equispaced wooden battens, which pass through notches in the division plate, extend between the ejector plate and tail plate in order to force off the tail plate when the bomb functions.
Mk II Body - The Mk II bomb body is identical to the Mk I except for the use of a different type suspension lug, and a light-gauge steel body which necessitates the use of a cast iron weight welded inside the nose.
Mk III Body - The body of the Bomb Mk III consists of a light-gauge steel tube which has a steel nose welded to one end. A cast-iron weight is welded inside the nose section. The after end of the body is closed by a tail plate held in position by three locating studs, which engage three slots in the after end of the body, and is secured in position by three brass rivets.
The tail plate has two bayonet slots and a hole to be engaged by pins on a transit base, or the securing screws of the Tail Unit No. 75 Mk I or Mk II. A V-slot in the skirt of the tail plate, aligned with one of the locating studs and diametrically opposite the hole, receives the locating pin on the Tail No. 75 to assure that the tail slot for the tail fuze lanyard is aligned with the suspension lug of the bomb. The suspension lug is of the same type used on the Mk II body.
The burster container is similar to that of the Bomb Mk I, but is welded to the ejector plate and internally threaded to receive the forward end of the central flash tube. The after end of this tube threads into the tail-fuze adapter, which is locked in place, and the whole assembly is secured to the tail plate by a locking ring.
The two layers of candles are separated by a division disc, and a priming system, similar to the one used in the Bomb Mk I, is used to ignite them. The candles are positioned as in the Bomb Mk I, but the wooden battens are not used, as the central flash tube serves to force off the tail plate when the bomb functions.
Mk IC Body - This bomb is very similar to the Mk III, but as it employs a Mk I body converted for tail fuzing, its body is of thick-gauge steel, and consequently the nose weight is dispensed with. The central tube is welded to the inner end of the burster container and is also welded to the ejector plate.
The Tail Units No. I Mk II, and No. 35 Mk I consist of a tail cone to which a cylindrical strut is attached by four fins. Three screws secure the tail to the tail plate of the bomb.
The Tail Assembly No. 75 Mk I consists of a tail cone to which a cylindrical strut is attached by four fins. Three screws attach the cone to the tail plate of the bomb, and a locating pin engages a V-slot in the tail plate to position the tail. An arming assembly, consisting of an arming spindle, arming vanes, and an arming-spindle fork, is also present. The Tail Mk II has cut-away fins to allow the arming vanes to be recessed for protection. Both the Tails Mk I and Mk II have inspection windows in the tail cone.
The bomb is suspended by a single lug, which is welded to the body.