It was certainly he who, early in 1631, opportunely brought up his regiment, which had large number of Irishmen, including his kinsman Walter Butler, to Frankfort-on-the-Oder, in Silesia, where the imperialists under Tiefenbach were awaiting the approach of Gustavus Adolphus at the head of a much superior force. Before the arrival of the Swedes, James Butler, in order if possible to obtain more soldiers and supplies for Frankfort, proceeded to the camp of Tilly, who was marching upon Magdeburg. Butler came too late, but he appears to have taken part in the Sack of Magdeburg, the result of which terribly avenged the fall of Frankfort. After the capture of Magdeburg and before the Battle of Breitenfeld he appears to have rejoined Tiefenbach, who had invaded Lusatia with such forces as he could command, but whom the news of the great defeat of Tilly obliged to retreat into Bohemia, where he occupied Nimburg on the Elbe, November 1631. A Saxon army under Arnim having taken position on the other side of the river, Butler was with his Irish regiment, as it is now called, sent across a wooden bridge to fortify and hold the bridgehead on the enemy's side; and his defense, ending with the burning down of the bridge, was so vigorous that finally Arnim returned to Prague.