As a matter of fact the Yankees had thoughts of coming quite soon. Possession of the town seemed to be desirable, in the first place, because for some time it was supposed to be the starting-point of a carriage-road to San Luis Potosí, and apparently could be made a more convenient base than the Rio Grande for a deep advance into Mexico; but the war department found before long that wagons and artillery could not cross the mountains by that route. In the second place occupation of Tampico appeared to be a logical feature of the Tamaulipas movement, in which Patterson was expected to play a leading rôle;[13.27] and moreover, Santa Anna himself had explained to Mackenzie that it would be advantageous as well as easy to make this conquest.[13.38] Conner had his eye upon the place, of course; but, aside from the question of overcoming its defenders, he felt considerable hesitation. It was regarded as the most dangerous port on the coast, and vessels could not ride out a gale at anchor off the shore. The bar, on which eight feet of water stood normally, had only a fathom in August, 1846; and as the fleet would have to rendezvous and prepare for battle in the open roadstead, he was afraid that one of the frequent northers would assail him before he could assail the town. September 22, however, when deciding upon the Tamaulipas expedition, Polk and his Cabinet agreed that Conner should attack Tampico, and the order was issued that day.[13.38] Santa Anna seems to have remembered the advice given to Mackenzie, and while at Mexico he instructed Parrodi to retire, if attacked, unless he could be sure of resisting successfully. On his way to San Luis he evidently received Marcy's intercepted letter of September 2, which announced that a movement upon Tampico was contemplated.[13.28] Hence on October 3, with a view to the confirmation of those instructions, he directed the war office to notify Parrodi of the American plan. Two days later the comandante general reported to Santa Anna that he could not defend the town victoriously, and explained in detail why. His garrison, including some 200 sick, consisted of less than 1200 men besides 200 available National Guards, ignorant of the use of arms. Only 870 of these men could be employed, according to a later statement of his, at the town and the bar, and having but 150 regular gunners he could not man the numerous and widely separated positions. Indeed he would not be able to subsist the garrison more than eleven days longer.[13.29] The enemy, on the other hand, it was said, included a shore party of 3000, and could attack by water and by land at the same time.[13.38] [TAMPICO EVACUATED BY THE MEXICANS]