Base your answer to the following question on the passage below and on your knowledge of social studies.

...A weary, exhausted, nerve-racked group of men it was indeed that, about noon November 1, assembled in a gully north of Sommerance[France] to rest and dig for the night. The artillery was still firing furiously, but the enemy's barrage[bombardment] had ceased very suddenly about 10:00 a.m. and now only occasional shells from long-range rifles would explode in the vicinty. The weather was gloomy and the moist air chilled one to the bones. Yet it was with that meticulous [methodical] care that is characteristic of worn-out men, that we prepared our foxholes, carrying boards and iron sheeting from abandoned machine-gunners' dugouts in order to make our ''houses'' as comfortable as possible, even though only for one night...

Source: William L. Langer, Gas and Flame in WW1, Knopf/Borzoi

Which means of warfare is described in this passage?
(1)guerilla
(2)nuclear
(3)biological
(4) trench