ambulances are wagons furnished by the several States and claimed as regimental property. If, however, they are available as ambulances, this is of little consequence; but there are other inaccuracies, as, for instance, in General Banks' division, where I know that 10 four-wheeled ambulances, new and of the army pattern, are or ought to be in possession of the quartermaster. In addition to this, I know that some of his regiments have four-wheeled ambulances furnished by their States. I regret that we have not received the returns of casualties at Fort Donelson, as they would assist me in estimating for the probable wants of this army. My estimate should be a minimum for several obvious reasons; still it would not be prudent to make it too small. The ambulance board estimated for 2 four-wheeled and 10 two-wheeled ambulances for a regiment. These would give transportation for 40 men, or 4 per cent. of the assumed force. At this rate we should have 500 four-wheeled ambulances for this army and 2,500 two-wheeled. This would require a train of four-wheeled ambulances 5 miles long, and yet it would carry but 5,000 wounded; whereas in a general engagement, with a force of 200,000 men, we might expect 60,000 wounded. If one-half of these require ambulance transportation, it would take 3,000 four-wheeled army ambulances to carry them, and the train would be 30 miles long. I mention all this to show how inadequate any attainable train must be to provide for possible wants. Let us have a reasonable train, and if needs be it must be sent back and forth as often as may be necessary to remove the wounded from the field to the hospital..

The two-wheeled ambulances are universally condemned, and we cannot rely upon them for the road. They are in my opinion indispensable as tenders to the four-wheeled ambulances. They can be run with comparative ease where it would be impracticable to carry a four-wheeled ambulance; therefore, to bring men off the field to the road or to the hospitals on the field or for any distance not exceeding 2 miles, they will be found very useful. Combined with thee cacolets and the hand-stretchers they will and must suffice for field purposes during an action. We have some 250 of these two-wheeled ambulances and about 200 cacolets. These in my opinion are sufficient of that kind of transportation for the army. The cacolet will answer for the road in case of necessity, and perhaps some classes of wounds might be transported to the hospitals in the two-wheeled carts.

I am furnished, then, with a basis fo 250 regiments on which to found my estimate for the four-wheeled ambulances. After much reflection I have concluded that one of these of the army pattern should be provided for each regiment or separate battalion. These would give transportation for 2,500 men (if 250 in number), and would make a train 2 1/2 miles in length. Upon the advance of course they would not be assembled in one body, but in sending the wounded back to the general hospitals it is possible they may be, and the train would then be as long and convey as many people as would probably be sent at one time to the hospitals. I would therefore respectfully recommend that the number of four-wheeled ambulances to be provided for the army be one to a regiment or separate corps, and that it be of the army pattern.

Very respectfully, your obedient servant,

CHAS. S. TRIPLER,

Surgeon and Medical Director Army of the Potomac.

General S. WILLIAMS,

Assistant Adjutant-General, Army of the Potomac.