The No 69 was the first British device to make use of the all-ways fuze later seen in the No 82 Gammon bomb, the No 73 Thermos bomb and the No 77 smoke grenade. The "Allways" fuze is an impact-only fuze. The term "Allways" refers to the fact that all of the possible ways in which the grenade could hit a target were guaranteed to trigger detonation. Normally, impact-detonated munitions must hit the target with a particular point of impact (i.e. perpendicular to the fuze mechanism) in order to detonate. In contrast, no matter which way the No 69 grenade hit the target (e.g. landing on its base, or sideways or upside down) it would still explode.
The All-ways fuze was composed of a free floating striker and detonator combination held apart by a weak spring. On top of this assembly was a steel ball bearing pressed against a conical housing by the striker. Any impact in the vertical axis would impart acceleration to either the striker or the detonator causing the firing pin to contact and ignite the detonator. Any impact in the horizontal axis would cause the ball bearing to follow the slope of the conical housing converting the horizontal acceleration into a vertical one touching off the detonator as before.
The fuze was worked by the user first unscrewing a plastic cap to expose a long, narrow cloth streamer with a curved lead weight attached to the end. Upon release from the hand or projector the weighted streamer would catch the air and quickly unwind from the top of the grenade eventually withdrawing a loose safety pin from the fuze. With the pin removed the striker and detonator would be free to come into contact, which would the happen due to the force of impact when the grenade struck a hard surface.
The all-ways fuze had a minor design defect in that the hard steel ball bearing would be propelled away from the explosion as a piece of shrapnel. When used in an "offensive" application such as the No 69 grenade where the user was not required to take cover before throwing, there was a chance that the user could be struck and injured by the fast moving ball bearing. According to military author Ian V. Hogg, this problem led to restrictions in the use of the grenade as practice ordinance.
Read more about this topic: No 69 Grenade