Noise discipline is the deliberate prevention and reduction of sounds a person produces through movement, equipment or communication. During evasion, the aim is to give the enemy as little audible indication of presence and location as possible. It includes securing equipment, controlling foot placement, keeping communication brief and taking listening halts, during which the person stops producing their own noise to hear the surroundings.
Movement, equipment and voice
A foot placed on a dry stick produces a short crack; metal parts striking each other may jingle with every step. Turning, bending or putting down a pack creates different contacts from walking straight ahead. The check therefore includes clothing, carrying straps and luggage. A cup striking another hard object inside a pack needs a different remedy from a stick breaking under a boot.
Voices, a watch alarm and a radio loudspeaker can reveal a location even while the person is stationary. Visual concealment does not stop these sounds. Someone sitting behind dense vegetation and talking has hidden their visible outline, but their voice can still reveal a person's presence to a listener.
Check and secure equipment
Before moving, check the equipment actually being carried for loose parts and hard contact points. At a suitable concealed location, a few careful steps, a bend and a turn can help identify movement-dependent jingling or rattling. Keep the check brief: a prolonged noise trial would itself attract attention. If a sound occurs only when putting something down, check that action again after correcting the cause.
Stow loose objects in available pockets so they cannot strike each other freely. Existing cloth can, for example, separate a cup from another metal object. Moving external parts can be secured with suitable straps or tape if available. Without extra material, a different packing position or putting a dangling item into an existing pocket may remove the contact.
After securing an item, check access and operation. A secured weapon sling must not obstruct moving weapon parts; important closures and necessary devices must remain usable. Switch off unnecessary hourly watch chimes. Do not indiscriminately disable a needed warning function simply because it is audible. After repacking or putting equipment back on at a halt, check the changed contact points again.
Foot placement, ground and pace
Choose the next foot position by its ability to support the load and by the possible noise source. Where possible, avoid loading small sticks, loose stones and pieces of ground that will tip or roll under weight. Place the foot lightly but securely; only a stable placement allows body weight to transfer under control. Dragging the foot or hurried corrective steps can displace material, break sticks or worsen an unstable footing. Where dense vegetation brushes clothing or a pack, account for that contact too.
The pace must leave enough time to perceive the ground and control the step. Darkness or ground that is difficult to inspect will often mean slower progress. A seemingly quiet surface may also be slippery. A fall creates noise and may cause an injury that prevents further movement. When danger or terrain requires rapid movement, careful packing cannot remove its movement noise; the person must account for that remaining indication in the next movement decision.
Necessary communication
In a small isolated group, speech is confined to what is needed for the next action or necessary information. Short messages to a nearby person avoid calling over a distance. The message must still be understood: a missed warning about hazardous footing or a misunderstood movement instruction can cause more movement and fresh noise. At a shared listening halt, everyone stops unnecessary movement, conversation and rummaging in their kit; one person’s noise can also hinder the others’ hearing.
If a radio is actually available, limit loudspeaker volume to what is needed for personal comprehension. The device should not broadcast received voices into the surroundings. The required communication must remain usable. A quiet loudspeaker changes only the audible component; a transmission may still be detected by electronic means.
What a listener perceives
Sound travels through air as waves. Whether a sound stands out also depends on the other sounds at the listener’s location. Wind can temporarily mask a sound. An enemy listener at an unknown position may, however, be closer to the source or in a quieter place. Barely hearing one’s own footsteps in the wind therefore describes only one’s own perception.
Vegetation and the ground affect propagation, as do the layers of air above them. If air near the ground cools while warmer air remains above, sound waves can be bent back towards the ground. Darkness therefore offers no acoustic protection; a wooded area is not a soundproof wall either. Listening conditions change with location and weather. A quiet impression at one’s own position cannot establish a fixed distance beyond which movement would be inaudible.
Listening halts and identifiable failures
At suitable concealed points, stop moving and listen for voices, footsteps, vehicles or other noticeable activity. This removes the interference from one’s own steps and equipment. If the same jingle returns when walking resumes, the contact point has not yet been corrected. A broken stick or a slipping object also calls for reassessing the movement itself and the surroundings.
After making a conspicuous sound, stop and observe as soon as the terrain and immediate danger permit. Nearby voices or movement provide new information for deciding whether to remain or continue. If there is no audible response, it remains unknown whether anyone was listening. An enemy can notice a sound and initially stay quiet.