Today mostly the domain of riverboat tours and kayakers, the Chicago River was once part of the thoroughfare for 28 World War II submarines built in Wisconsin making their way out to the Pacific. To highlight this little-known chapter of Chicago history, two Illinois submariner veterans groups are raising money to erect a memorial along the riverwalk.

"It's a part of the city's history that most people today are not aware of," said Frank Voznak Jr., project manager and vice commander of the northern Illinois Crash Dive Base, which is teaming up with the USS Chicago Base. "We want to try to educate the public on what did happen all those many years ago."

In summer 1941, in anticipation of involvement in World War II, the U.S. Navy approached shipyards across the country about building submarines. Among those contacted was the Manitowoc Shipbuilding Co., which had never built submarines but agreed first to build 10, then eventually 30, said Karen Duvalle, submarine curator at the Wisconsin Maritime Museum in Manitowoc, 40 miles southeast of Green Bay. The museum has been working closely with the veterans groups.

The Manitowoc River was too narrow for a typical launch, so the submarines had to be side-launched, a process that involves sliding a vessel off its supports and tipping it into the water on its side, Duvalle said. Before the submarines were sent off, crews did "sea trials" on Lake Michigan and tested diving, surfacing and other system controls.

"People are pretty surprised that such a unique vessel was built in Wisconsin," she said. "They usually associate (submarines) with East Coast shipyards. But a lot of people think it's pretty neat that we built submarines here ... and that they were some of the best built submarines in the Navy at the time."

Back then, the St. Lawrence Seaway did not exist, so the Manitowoc company chose the best route available that could accommodate the 312-foot-long vessels: through Illinois and down the Mississippi River.

The submarines were loaded onto floating dry docks, which could be lowered slightly underwater to fit under bridges, and pulled by tugboats down the Illinois River to the Mississippi River to New Orleans to the Gulf of Mexico through the Panama Canal and, finally, to the Pacific.

It's possible that even Chicagoans in the 1940s were, at least initially, unaware of this because of government secrecy in the face of a raging world war.

A Chicago Tribune article dated May 27, 1945, had the headline "28 Subs Built at Manitowoc, Navy Discloses" and detailed "for the first time" how the submarines were made (assembly line-style and in sections to allow for inland construction) and how much the subs cost (more than $100 million). It also named other Wisconsin and Minnesota shipyards that were building Navy watercraft.

This secrecy explains why photos of the submarines traversing the Chicago River are rare; the subs were usually sent early in the morning to avoid attention, Duvalle said.

By the time the war ended, the Manitowoc company had built 28 of the 30 Navy-ordered submarines; of those, 25 saw action and four were lost, crews included.

It was a World War II submariner who inspired the idea for a Chicago memorial. Harry Alvey, 90, had been talking with younger veterans at an event in April 2010.

"I challenged them to make something that would recognize the 28 boats (built in Manitowoc) and four that were lost," said Alvey, of Wausau, Wis. "I didn't tell them what to do; I just gave them a challenge. You don't tell submariners what to do. You trust, and they take it from there."

His fellow former submariners went to work. In January 2011, Voznak connected with members of the USS Chicago Base about creating what at the time they imagined would be a simple plaque to post along the Chicago Riverwalk.

But months later, when the project was proposed to Ald. Brendan Reilly, who represents the tourist-heavy 42nd Ward, Reilly encouraged the groups to think bigger.

"I thought certainly the plaque is appropriate, but why wouldn't we want to make this more of a landmark destination for people to pay their respects to the veterans who've served our country?" Reilly said. "So when they were able to come up with this very modest bulkhead design, I thought that was a fantastic idea."

The new plan for the memorial, which they hope will be located east of the Columbus Drive Bridge, juxtaposes past and present, Voznak said. It consists of a reproduced submarine inside wall, or "bulkhead," with a real watertight door salvaged from the USS Trout. The door will be welded open so visitors can sit on one of two benches facing it, look through and see the Lake Shore Drive Bridge, through which the submarines passed more than 70 years ago.

Many elements of the structure are symbolic; for example, the benches will be made of teak, the kind of wood from which submarine decks were traditionally made, and will have steel backings coated with marine-grade epoxy paint and perforated with drain holes to represent the superstructure, or the part of the submarine that protrudes above the deck.

Although Reilly supports the idea, he said the veterans groups need to secure funding before reconvening with the city to make it official. So far, the groups have raised $12,000 of their $250,000 goal for the cost of the design, construction and other fees. Tom Sasgen, treasurer of the USS Chicago Base, said many of the donations have been from other veterans groups. Sasgen said the groups are in the process of sending letters to corporations asking for help.

For instructions on how to donate, visit the Chicago memorial page at crashdivebase.com.