They form a crescent. They anchor it at one end and sweep on, until they've cleared a quadrant. Then they anchor the opposite end and reverse direction.
15 seconds sound clip from the The War of the Worlds (1953) movie soundboard.
You can hear this line at 00:54:30 in the DVD version of the movie.
Quote context
[...]
- Urgent. Major Bentley Dawson, report to General Mann.
- Make every effort to contact the civil authorities...
- They slash across country like scythes, wiping out everything that's trying to get away from them.
- That explains why communication is cut the moment their machines begin moving.
- Nothing more's come through.
- Same thing that happened on the Pacific coast.
[...]