position, 1,000 men, in addition, should be added to guard the rifle-pits (about 1 mile long); and this latter number may need to be increased from the reserves in case of a prolonged attack.
The artillery garrisons of all the forts should be kept full. I have calculated for three reliefs of gunners for all the guns. This provides for contingencies, and the artillerymen are counted as part of the garrison, as all not serving guns would be subject to man the parapets in case of assault; 10,305 men are necessary for this purpose.
There should be at least infantry enough to fill up all the garrisons of all the works south of the Potomac; to supply an additional 1,000 men at Fort Lyon, and 2,000 at the Chain Bridge, and a reserve of 15,000 men, besides 2,000 or 3,000 cavalry and eight or ten batteries of artillery, making 35,000 men in all, besides cavalry and field artillery; and this is the very lowest estimate for defense, under the most favorable circumstances, as will be seen hereafter.
If the enemy was in front of Washington in force, and the Potomac was low, we might expect him to threaten both sides, and it would be necessary to have the works between the Potomac and Eastern Branch fully garrisoned.
Finally, should he establish himself in force on the north side of the Potomac, we might expect formidable assaults upon the works over the Eastern Branch, unless they were fully garrisoned. In general, however, the defenses of part of the works might be safely trusted to their artillery garrisons.
The following extract from the report of the commission ordered last autumn by the Secretary of War to report on the Defenses of washington may be interesting:
The total infantry garrison required for their defense, computed at 2 men per yard of front perimeter, and 1 man per yard of rear perimeter of works, is about 25,000. The total number of artillerymen (to furnish three reliefs for each gun) required is about 9,000. It is seldom necessary to keep these infantry supports attached to the works. The artillerymen, whose training requires much time, having learned the disposition of the armament, and computed the distances of the ground over which attacks may be looked for, and the ranges and service of their guns, should not be changed; they should remain permanently in the forts.
The 25,000 infantry should be encamped in such positions as may be most convenient to enable them, in case of alarm, to garrison the several works, and a force of 3,000 cavalry should be available for outpost duty, to give notice of the approach of any enemy.
Whenever an enemy is within striking distance of the capital, able by rapid march to attempt a coup de main, which might result in the temporary occupation of the city, the dispersion of the Government, and the destruction of the archives, all of which could be accomplished by a single day's possesion, a covering army of not less than 25,000 men should be held in position, ready to march to meet the attacking column. Against more serious attacks from the main body of the enemy, the capital must depend on the concentration of its entire armies in Virginia or Maryland. They should precede or follow any movement of the enemy seriously threatening the capital.
You will observe that from Hunting Creek north to the Potomac there are about 11,000 yards of rifle-pits. As observed elsewhere, it will never be necessary to man the whole at once. Take that part be tween Hunting Creek and Four-Mile Run, for example. There are 5,100 yards of rifle-pits connecting the works, but the actual front before which the enemy could arrange his line of battle will not be more than 2,100 yards. He will not mass his men in the valleys, or on the slopes of the valleys of these streams, where they would be seen and cut up by plunging and cross-fires of our forts. He may try their flanks with small columns, favored by darkness, &c., and they would be resisted by the fire of the forts, and by a few men holding the pits until reserves could be brought up.