Groton — The tin lunchbox was precious cargo.

During the two-hour flight from Chicago to Hartford, it sat in a plastic shopping bag on the lap of Michael Brahill, who on Friday donated this prized possession of his younger years to the Submarine Force Library and Museum in Groton, which includes the Historic Ship Nautilus.

What makes the lunchbox unique is the images emblazoned upon it: the Nautilus, the USS George Washington, the USS Skipjack and the USS Seawolf.

The lunchbox was produced in 1960 by the American Thermos Bottle Co. factory in Norwich.

The big factory off Route 12 in the Laurel Hill section of the city was converted into condos in the 1980s.

Norwich historian Dale Plummer could not confirm how many of these lunchboxes were produced, nor how long the company produced them.

Brahill, who lives in Chicago, originally thought he used the lunchbox throughout grammar school, but said that couldn't be possible, given the production date.

He suspects he used it during the second half of eighth grade, and said he certainly remembers carrying his lunch in it.

He'd always wondered what became of it.

About two years ago, he discovered it as his mother's house.

"I thought it had disappeared but my mother tends to save everything," he said Friday while standing in the museum with the lunchbox before handing it over to a staff member there.

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After visiting the museum in January, Brahill realized that was the most appropriate home for the lunchbox.

Since finding it, he'd been storing it in a closet at his home.

Lt. Cmdr. Ben Amdur, officer in charge of the Historic Ship Nautilus and the director of the museum, said the museum receives hundreds and even thousands of offers of donations each year.

The museum took custody of the lunchbox Friday, which began the process of considering it as a donation.

A collections committee reviews each item once it is in museum custody, and determines whether it would be a suitable donation based on how unique it is, its historical significance and the museum's ability to store and maintain it, among other criteria.

If it meets the committee's standards, it goes to Amdur for approval. The Director of Naval History must ultimately approve the item unless it's valued higher than $5,000, in which case someone higher in the chain of command must approve it.

While to the average person Brahill's donation may seem to be "just a lunchbox," Amdur said. "It tells how important it was to pop culture at the time ... it helps place it in a historical context."

j.bergman@theday.com

Twitter: @JuliaSBergman