PENSACOLA HARBOR, FLA., February 7, 1861.

Col. L. THOMAS,
          Assistant Adjutant-General, U. S. Army:

SIR: I have the honor to report that I arrived on this station yesterday in the U. S. steamer Brooklyn, with Company A, First Artillery. I met orders here which prevent the landing of my company or the re-enforcement of the garrison of Fort Pickens at present. Yesterday I landed at Fort Pickens, assumed command of the forces on the station, inspected the defenses, and had a consultation with Lieutenant Slemmer. I am compelled to remain on board the Brooklyn for the present, and can, of course, only give general instructions to Lieutenant Slemmer. I am sorry to inform the Department that I found Fort Pickens in a very inefficient state of defense. At the time Lieutenant Slemmer removed his command to Fort Pickens there were only forty guns mounted in the fort. At present there are fifty-four in position. The accompanying sketch [not found] indicates the position and class of guns now in position; total, fifty-four of all kinds.

Lieutenant Slemmer has with him only forty-six enlisted men for duty, and thirty ordinary seamen from the yard at this station, and the latter are entirely untrained, insubordinate, and of but little use in case of attack. There are fifty-seven embrasures that are unprovided with cannon, and are only about seven feet from the bottom of the ditch, and at present but few of them have only the common wooden shutter, presenting only a slight obstacle to an enemy. There are only very imperfect means of barricading them. Such as they are, however, I have given orders to be immediately employed.

Lieutenant Slemmer has been obliged to employ his command in getting guns into position and in barricading the embrasures. He is obliged to keep one-half of his men under arms every night, and they are nearly all exhausted with fatigue. The guns and carriages and implements are all old, and nearly unserviceable. I have made a requisition direct on the Department for the necessary supply of guns, carriages, and ammunition. The supply of this last is very inadequate. There is no ammunition for the columbiads, no cartridge bags for them, nor flannel to make any. In fact, had it been the intention of the Government to place the fort in the state to render its defense impossible, it could not have been done more efficiently than it has been done. The post is without any medical officer, and if it is intended to defend it there should be an Engineer officer sent at once to the station. I trust that the Department will immediately order that the supplies requested be sent. There are no bunks either for the hospital or for the troops, and but little bedding for the sick. I request a supply may be sent. There are plenty of provisions for the present, although I should like some desiccated vegetables and supplies for the officers. I would mention that all of the troops will be compelled to live in open casemates, and many of them will soon be on the sick-list.

The seceders have a considerable force in and about Pensacola; what number I am unable to say positively, but they are estimated at about 1,700 men. They are disorderly, and very unwilling to be controlled. Their leaders, from what I can learn, I believe are sincere in their intention to observe the armistice, but their ability to control the men under their command is very doubtful. They are engaged in erecting batteries, are making sand bags, &c. They have plenty of means of transporting their troops to Santa Rosa Island, and can attack the fort on all sides at once. At present there is not one trained man to a gun within the fort. Should the enemy decide to attack, it is exceedingly probable that he might succeed in penetrating into the fort before my company could be landed or any succor could arrive from the fleet. I should therefore urge upon the Department the necessity of the fleet taking up a position such as to prevent the landing of any forces within one and a half miles of the fort; this would give time to provide for the defense of the work and the landing of the troops from the fleet; otherwise we may have the mortification and disgrace of seeing the fort taken by a body of untrained troops under our very noses.

Should the armistice be broken, my company, all the marines, and as many sailors as may raise the garrison to four hundred men should be immediately landed. All of the advantages of the present armistice are entirely on the side of the seceders. I would therefore urge upon the Department the necessity of immediately re-enforcing the garrison. The two additional companies ordered to Forts Taylor and Jefferson are not immediately required for the defense of those works. In fact, in their present state, and with the forces now in them, they would be stronger than Fort Pickens will be when garrisoned with four hundred men. Captain Meigs kindly offered his services, if necessary, to assist in the defense of this place, and I request the Department that he may be ordered to repair to this place.

Lieutenant Slemmer has done all that it has been possible to do with the small force under his command. His resolution to defend his post at all hazards evinces the highest moral courage on his part, but at the same time I must state that with any amount of vigor on the part of the assaulters his defense would have been hopeless. His resolution has probably been the means of preserving Fort Pickens from the seceders.

Yours, &c.,

I. VOGDES,

Captain, First Artillery.

P. S.--I must not be understood as recommending any violation of the existing armistice, but the collection of an amount of troops on the station as may be necessary for the defense should anything occur to rupture the present armistice.