Day by Day Journal, Page 49, Trent Affair

"Mason + Slidell taken by Federals @ Bermuda"

This refers to the Trent affair, in which Confederate diplomats James Mason and John Slidell were captured by Union forces from aboard a British vessel en route to England. The North and leadership aboard the Union vessel felt justified in capturing the two ambassadors due to their status as Confederate representatives seeking international recognition; however, the British government saw the action as an infringement on British sovereignty and neutrality. In response, the British government threatened war, backing off only once Lincoln disavowed the captain’s actions and released the two Confederates.