midnight
`` No movement could have been more acceptable to Armistead , and he quickly took advantage of it , ordering a general cannonade and bombardment from every part of the fort , thus punishing the enemy so severely that in less than half an hour he fell back to his old anchorage . `` One of their rocket vessels was so badly injured that , to save her from being entirely destroyed , a number of small boats had to be sent to tow her out of the reach of Armistead 's guns . The garrison gave three cheers and ceased firing . `` The British vessels returned to their former stations and again opened fire , keeping up , with very little intermission , a furious bombardment until past midnight , when it was discovered that they -LRB- the British -RRB- had sent a pretty large force up the Patapsco to capture Fort Covington , commanded by Lieutenant Newcomb , of the United States Navy , and the City Battery , then attack Fort McHenry in the rear . For this purpose there had been sent one thousand two hundred and fifty men in barges , with scaling ladders and other implements for storming the fort . But providentially their errand was made known to the garrison of Fort McHenry in good season by the throwing up of rockets to examine the shores , and not the fort alone but also two redoubts on the Patapsco immediately opened a heavy fire upon them , and drove them away . `` So heavy was the firing that the houses of Baltimore were shaken to their very foundations .