This card is an image of the SS Frank Purnell, originally named SS McIntyre. It was a bulk freighter built in 1943 to support increased production for World War 2. It is categorized as a type L6-S-B1 bulk freighter.

The caption states
THE SOO LOCKS
Sault Ste. Marie, Michigan

A giant lake freighter completely fills the MacArthur lock, where is will be lowered 20 fee to Lake Huron level before steaming on its way. Seen here from the visitors observation tower provided by the U.S. Corps of Engineers, which organization operates the Locks. One can almost reach out and tough the freighters. It is an excellent place for camera fans to get pictures of the never-ending procession of freighters, and some passenger boats. – Photo by Lucy Gridley

–This particular freighter is still in existence at the time of this posting, It was used as a barge and is now laid up on the Calumet River in Michigan.

This post card likely dates from the 1950s.