On this day, the two propeller steamships, the Exact and the Alliance, continued sailing east through the Gulf of Mexico toward New Orleans with the 16th Ohio and 49th Indiana on board. Sometime on this night, the Alliance was approached and fired upon by the United States warship U.S.S. Tennessee. Reports indicate the Tennessee fired five shots at the Alliance before the two ships realized they were both Union. Cpl. Theodore Wolbach describes the event:

Our regiment went aboard of two propellers--the right wing on the Exact, left wing on the Alliance. The Exact run through to New Orleans without incident. The Alliance was not so lucky. When well on her course, she was chased, fired at and brought to by a strange craft that proved to be the U.S. man-of-war Tennessee. Each was mistaken in the other. The latter was thought to be the privateer Alabama, and the former was supposed to be a blockade runner.

Wide view modern day map showing the estimated route and location of the 16th Ohio, on board the steam propeller ships Exact and Alliance, on its voyage from Matagorda Island, Texas, to New Orleans, Louisiana, April 18 and 19, 1864.
A - Matagorda Island, Texas, where the 16th Ohio boarded steamships bound for New Orleans on April 18, 1864.
B - Highly estimated location of the steamships carrying the 16th Ohio back to New Orleans on the night of April 18, 1864.
C - Highly estimated location of the steamships carrying the 16th Ohio back to New Orleans on the night of April 19, 1864.