Explanation: In WW1, novel and daring tactics were developed as part of a pattern of 'trench raids', wherein small groups of highly-motivated troops would assault an enemy trench by surprise, clearing it out, either for later troops to hold, or just to damage and demoralize the enemy.
While firearms were still widely used in these attacks, especially pistols, shotguns, and the then-new submachinegun, many trench raiders found that the most effective tools were speed, stealth, grenades, and a positively medieval level of close-combat. Crawl up to grenade throwing range, saturate the trench with grenades, then go in and finish off the dazed occupants. Canadian forces were noted to be particularly good at trench raiding.
On the Western Front, brass knuckles, maces, and spikes were used; on the Italian Front, the Italian Arditi, a kind of proto-special forces, used narrow daggers - stereotypically held between the teeth to keep the hands free and allow a grenade to be thrown first.
The Arditi, in particular, prided themselves in charging before the grenade exploded - timing their charge so that they would be just before the lip of the trench when the grenade went off. This was highly effective - having some lunatic with a knife on you 0.4 seconds after an explosion is a hard thing to fight off - but it was also noted to lead to casualties during training. If your timing is off, the momentum of being at a full dash towards a trench is unlikely to allow you to skid to a halt for the 0.2 seconds you need to not get blasted in the face by your own grenade, like every other poor bastard in the trench! That's timing that needs practice - and practice was hard to do with anything except live ammunition...
