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120mm mortar shell fitted with an M734 Fuze
American soldiers firing a 120 mm mortar

The M734 Multioption fuze for mortar shells uses frequency modulated continuous wave (FMCW) directional doppler ranging (DDR) techniques and is hardened against electronic countermeasures designed to prematurely trigger detonation. Electrical power is supplied to the fuze via an air flow driven turbine alternator.

The M734 fuze is used on 60 mm, 81 mm, and 120 mm mortar projectiles. The updated version is the M734A1.

Safety/Arming Mechanisms

The fuze has three safety/arming mechanisms: initial arming is via setback (>395 gs), accompanied by a velocity change of 70 ft/s sustained airflow to the turbine alternator for a minimum of 100 metres, coupled with apex detection for delayed electrical arming[1].


Tools are not required to arm, disarm or configure the M734 fuze. There is no pull-wire safety pin to remove, unlike some other mortar fuzes. The M734 can be adjusted simply by rotating the top of the fuze clockwise by hand until the required 3-letter setting is over the index line. Additionally, the detonation setting can be changed any number of times before firing, without causing damage to the fuze.

There are four sets of 3-letter codes engraved around the circumference of an M734 fuze which have the following meanings:

  1. PRX - proximity air burst between 1 and 4 metres (3 to 14 feet) above the target
  2. NSB - near surface-burst between 0 and 1 metre (0 to 3 feet) above the target
  3. IMP - impact i.e. instantaneous detonation upon hitting the target
  4. DLY - delayed detonation, 0.5 seconds after impact

Note: the PRX setting will detonate a 60/81mm mortar shell at a height of 7 feet (2.1 m), and a 120 mm shell at a height of 14 feet (4.3 m) above the target.

Reliability is increased by the fact that if the M734 fails to detonate the mortar shell at one setting, it will immediately and automatically use the next one along i.e. failure at the PRX setting causes NSB detonation to be selected. Similarly, failure to detonate at the NSB setting would automatically cause IMP to be selected, and so on.

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