Imprisoned in Tripoli, Captain William Bainbridge wrote more than a dozen letters to Tobias Lear, the United States Consul General to Algiers. This letter in particular is dated April 30, 1804 and notes the death of an unnamed Seaman, the dire need for clothing, and his anxiety at not having heard from Commodore Preble or any American official in over a month.

However, on the reverse side is a secret message written in lime juice. This technique, called sympathetic ink, has been used throughout the world for centuries. A note written by American official George Davis on the address side of the letter directs Lear to “scorch this letter…over a hot fire.”  The contents of the invisible ink convey a much different tone. Rather than passively awaiting freedom, Bainbridge estimates the number of troops necessary to attack the Pascha, provides ideas on how to negotiate with his captors, and names an ally in the Tripoline government who is willing to help for “a generous fee.”

Half of the letters penned by Bainbridge from prison contain invisible ink messages with similar suggestions on how many thousands of dollars the Pasha would accept as payment for peace and his continuous attempts at getting Tripoline officials to pressure the ruler for peace.

Up until two months before he was released from prison in June 1805, Bainbridge was still writing secret messages. It is unknown whether Tripoline forces were none the wiser to Bainbridge’s secret message or had deemed the contents of the invisible ink innocuous. However, a note (in sympathetic ink) in a letter dated December 19, 1804 may provide a clue as to whether the Tripoline forces had knowledge of the secret letters: 

Dr. Sir, This letter is a duplicate of one I wrote you on the 13th Ulto, which was well covered with juice; – but it was destroyed by our chief gard; I have however sent you the contents of the invisible [ink] Blank. (2147.9)