What's new
British Ordnance Collectors Network

This is a sample guest message. Register a free account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members through your own private inbox!

US 123A1 long delay tail fuze

pzgr40

Well-Known Member
Premium Member
Cutaway model of an US 123A1 long delay tail fuze with anti-withdrawal device, as used in US GP bombs, ranging from 100 Lb to 2000 Lb and 500 and 1000 LB SAP bombs.

Functioning of the fuze:
Upon release from the bomb rack, the arming fork is withdrawn from the impeller of the fuze (impeller is missing). After appr. 4 to 6 turns of the thread of the arming stem the glass ampoule is broken , 5 to 6 turns more seals the fuze , i.e; the stem collar is flush against the rubber retainer washer. A locking nut on the thread enshures the threaded part can only move a desired distance. The spring loaded firing pin is kept in position by a ring of bearing balls which fall under the countersunk head screw part of the firing pin and are kept in inward position by the celluloid ring around the balls. As soon as the celluloid ring has been sufficiently dissolved by the aceton, the balls can move outward, releasing the firing pin into the Firing cap M16A1.
The delays are factory set by means of varying the number of celluloid discs and the strength of the alcohol- aceton solution. Set times are (in hours); 1, 2, 6, 12, 24, 36, 72 and 144 hours.
A locking ball is placed in a groove on the outside of the fuze. When the fuze is inserted into the bomb it will roll on the inside of the booster housing. If however attempts are made to screw the fuze out of the booster, the ball -which will have rolled in the lower position due to gravity- will act as a locking device. As a result of this, one starts to unscrew the upper part of the fuze body from the lower part of the fuze body, allowing the balls surrounding the spring loaded firing pin retainer to move outward after unwinding the upper and lower fuze body 1 ½ turn (3/32” or 2,38mm). This allows the firing pin retainer to move downward, pressing the firing pin into the firing cap, detonating the bomb.

One should take into consideration that bombs with this fuze inserted cannot be disarmed in any way, even if the bomb is not thrown or armed. Therefore bombs that are not used are to be released over enemy territory or over sea.


There are three different types of this fuze, only differing in length of the arming stem;
M123A1 - 9,39” (236,2mm)
M124A1 -12,39” (314,7mm)
M125A1 – 16,39” (416,3mm)

It must be noted that the fuze resembles the British No.37 fuze in technical design and functioning.

Regards, DJH
 

Attachments

  • Fuze US 123A1 long delay tail fuze.jpg
    Fuze US 123A1 long delay tail fuze.jpg
    263.1 KB · Views: 75
  • Fuze US 123A1 long delay tail fuze detail.jpg
    Fuze US 123A1 long delay tail fuze detail.jpg
    251.1 KB · Views: 87
Last edited:
Post war version with 36 hours delay
 

Attachments

  • 20180524_205230.jpg
    20180524_205230.jpg
    290 KB · Views: 51
The British Post War version (Bomb Tail Fuze 79, Mk2 & Mk 3 Acetone, the relevant Technical Publication being T549460) was an improvement. There was always a danger that the glass acetone container was shattered in transit, so this fuze had a device which locked the device if this had occurred. Unfortunately, the Technical Publication in question has gone "AWOL", so I can't show details!
 
Top