ii. By sinking pits close to the front crest of a feature

(_See_ Fig. 35).

12. In some circumstances guns may have to be entrenched under cover of darkness in readiness to open fire at daylight. Careful preliminary reconnaissance is the chief essential to avoid mistakes in carrying out the various works (_See_ Sec. =189=), special care being taken to make sure that the principal line of fire is laid out correctly.

While the nature of the soil, the proximity of the enemy and the time available will all have their influence on the details of the works, every endeavour should be made to conceal them from view.

=239.= _Passage of obstacles._

1. The obstacles likely to be met with will vary from walls or ditches to unfordable rivers. In the case of the smaller obstacles a few minutes’ use of the tools carried with the battery will often be all that is required.

2. Obstacles should be crossed at right angles and in column of route, as each carriage will make the way easier for the one which follows. In the case of boggy places, however, each carriage should cross at a different spot. The gunners should always be dismounted from the carriages if there is any likelihood of the latter being overturned.

3. For the passage of small ravines a serviceable bridge can be quickly made by using a pair of wheels on their axle to support the road-bearers. _See_ Fig. 36.

If the bottom of the ravine is soft, two spars, D and E, should be lashed to the wheels as shown. The wheels are then lowered, hauled into position, and secured by guys AB, BC.

One or two transoms (H) are then lashed across the top of the wheels with square lashing and the road-bearers (R, R) placed in position. The number of the latter depends on their strength and on the weight to be passed over.

Transoms 4 × 9 inches (8 inches in mean diameter if round) and 5 road-bearers, mean diameter 6½ inches, will bear field guns and howitzers. The road-bearers should be butted against pieces of timber (F, G) sunk in the ground.

If planks are procurable to form the roadway, they should be used. If not, the road-bearers must be placed close together and covered with branches of trees and brushwood. If horses are to cross the bridge, it should be covered with earth to deaden the sound.

4. Plate VII shows another type of bridge constructed with stores, most of which are carried with a battery.

5. Should it be required to pass field guns across a river quickly, the gun and carriage can be floated across by means of four casks lashed as shown in Plate VIII.

The number of casks required can be calculated from the following rule:--

The available buoyancy of a cask (_i.e._, weight which it will support) in pounds is found by multiplying its contents in gallons by 9. Thus a 108-gallon cask has an available buoyancy of 972 lbs.