Model 35 was the name of a series of hand grenades used by Italy during World War II.
The first grenade, the O.T.O, was the simplest of the three grenades in the series and it weighed 150 grams. The diameter of the O.T.O. is also about fifty-five millimeters and the explosive used in it was trinitrotoluene. In order to arm the grenade, one must first remove the black tab on the side of the grenade just as one is about to throw the grenade. This process of removing the black tab unlocks the special safety lever which arms the grenade. Although, the grenade needed to be in the air for quite some time to allow the mechanism to work and even so, it was not very reliable.
The mechanism worked as in the following, in the top of the O.T.O was a lead ball that was designed to push the striker into the primer, but it was hindered by a safety bar. While the grenade was being thrown, it is supposed that this safety bar would be removed while in the air because it is connected to the safety lever which is supposed to fall out with the force of the throw, allowing the striker to hit the primer when the lead ball hit the striker itself. This would occur during impact. The grenade was designed to detonate on impact and the "always" fuze is also designed to detonate regardless of how it hits the target. The blast radius of the O.T.O. was about fifteen meters.
The next grenade in the series was the Breda version. It operated the same as the O.T.O. in that the safety bar would supposedly be removed while in the air and that the grenade was armed with a black tab on the side of the grenade, but the Breda's safety bar was not held as firmly in place as with the O.T.O.. This design feature was incorporated in an attempt to increase reliability. The Breda also had the same TNT explosive as the O.T.O and a slightly heavier weight of 180 grams. The Breda was not extremely different from the O.T.O., but it did include more parts in its detonation mechanism making it more complicated. The final grenade in the Model 35 series of grenades was the S.R.C.M..
The S.R.C.M. had a shorter blast radius of twelve meters rather than the fifteen meter range of the O.T.O. and the Breda and it is the most complicated of the three. It had a modified safety bar and a new fail safe mechanism that requires a certain amount of force to detonate. This means that it is less likely for an accident to detonate the grenade. Like many other grenades, there are versions of the Model 35 series' grenades that are designed for training purposes. There are also smoke versions of the three grenades.
The Model 35 series saw use in North Africa where it was used against British and Commonwealth forces. They nicknamed the grenades "Red Devils" most likely because of the bright red color scheme. Some German forces also used the Model 35 series and they were redesignated. The O.T.O. was redesignated the Handgranate 327 (i), the S.R.C.M. was redesignated the Handgranate 328 (i), and the Breda was redesignated the Handgranate 329 (i). Some versions of the Model 35 were used up to the 1990s.