Silas was a Naval officer who died on the British prison ship Jersey in New York Harbor. He was 39. Sources:MA. Sold. & Sail in the War of the Revolution, 17 Vols.He is listed in Vol. 4, p. 706. And Continental Marine Corps Officers - 1775-1785.
His parents were Jonathan Devol, Sr. b. 1711 Dartmouth, Bristol, MA Colony, d. 1782 at Tiverton, Newport, RI Colony. There is a photo of him on Find-A-Grave.
Some other sources:Prescott Hildreth, "Sketches of Early Ohio Pioneers" and Herbert Devol, "Devol, Early Settlers in RI 1639 and in OH 1788", pub. 1997.
Silas went to France on secret missions during the war.
There is a LOT of history on Silas, including the Devol family on Ancestry listed under Public Family stories, with sources.
If you don't have subscription to Ancestry and don't want to pay the full freight, they offer 14 days free from time to time.Worth the look.