This is carefully explained in a letter by Staff-Sergeant Barlow, R.A.M.C., to the Vicar of Prestwich. "Perhaps it would be well to explain where our work as a field ambulance comes in. We are not in the sense of the word a hospital. In the first place a regiment is in the trenches, and in close proximity to the trenches, the regimental bearers carry their wounded to some place of cover or comparative safety, such as a barn or farm-house, or in the case of a town being shelled, cellars are used. These are called Regimental Aid Posts.
"As a Field Ambulance we follow from one to two miles in the rear of the firing line and form dressing stations, using schools or barns for the purpose. Our ambulance waggons and stretcher-bearers go out under cover of darkness to collect from the Aid Posts the wounded soldiers, the waggons halting perhaps half a mile away, while the bearers cross fields and roads to the Aid Posts where the wounded soldiers are.
"This is very dangerous and requires much caution; lights are prohibited, as even the flare of a cigarette becomes a good mark for the enemy's snipers, of whom they appear to have many.
"Each regiment forms its own Aid Post. One ambulance unit attends a brigade. After the wounded are brought to the dressing station, the wounds are redressed, and the soldiers are as soon as possible despatched to the clearing hospitals at the base."
Staff-Sergeant Barlow proceeds to describe his first impressions of this awful work:
"What were my first impressions? you may ask. They were such as I can never forget. We were halted near a farm-house, the tenants of which had cleared out, leaving fowls and pigs unattended. The pigs could not have been fed for several days, as they were shrieking for food; we called it crying. The pigs were fed with food from the lofts. Dinner was served to the men (army biscuits and jam), in the midst of which an order came for an ambulance waggon for a wounded man.
"We were all astir, and it was the first casualty we had had to deal with. The waggon went out, and later several stretcher squads and other waggons. The remainder had to fall back about half a mile to a small village to prepare a school and church for the receipt of the wounded.