The architecture firm Miller Dunwiddie, celebrating its 50th anniversary this year, can claim a key place in the development of the Twin Cities.

Founders Bill Miller, Foster Dunwiddie and Ken Whitehead opened the business in a storefront at Bloomington's Southtown Center in 1963. Now housed in offices in Minneapolis' Warehouse District, it is one of the few firms of that era to still thrive today.

When the business started, it hit a cultural home run right off the bat: One of its first jobs was designing a series of circular, glass-walled Midwest Federal Savings & Loan branches, which instantly became icons of 1960s Twin Cities suburbia.

But of its early accomplishments, the one with the most impact was its 1968 design of a new hangar at Minneapolis-St. Paul International Airport, which was later converted into the airport's first international charter terminal. The firm also was the architect behind the 2001 upgrade of the charter facility into the 10-gate Hubert H. Humphrey terminal (now rechristened as Terminal 2) and its adjacent parking ramp.

That transportation legacy — which first began with the involvement of Miller and Whitehead in the design of MSP's Lindbergh terminal in the late 1950s — still accounts for much of its business, said Mark Miller, the firm's COO and son of Bill Miller.

"We're still doing a lot of transportation work, particularly in aviation," he said, estimating that up to half of the 40-employee firm's $9 million in annual revenue comes from that sector.

In recent years, that transportation work has expanded to include light-rail projects.

"The work we did on the parking ramps of the [Humphrey terminal] led to us doing the Blue Line light-rail station there," firm co-principal Chuck Liddy said.

That, in turn, put the firm in position to land further jobs along the Twin Cities' first light-rail line, including designing the extensions of 10 of its stops to accommodate three-car trains as well as laying out its Target Field station.

"Now we're working on the east half of the [proposed] Southwest Corridor light-rail line," Liddy added.

Along with its transportation specialty, another thread first established 50 years ago remains constant in the firm: the renovation of historic structures, particularly churches and other religious facilities. That was a keen interest of founder Foster Dunwiddie and has continued through recent years with large-scale renovations of the Cathedral of St. Paul and the Basilica of St. Mary in Minneapolis.

Its renovation work also has included the Minnesota State Capitol and historic classroom buildings at the University of Minnesota and in the Minnesota State Colleges and Universities system.

And in a spinoff from its renovation business, Miller Dunwiddie also has developed a so-called "building envelope" service, which has served to diversify its capabilities and helped keep income robust during the economic downturn.

"What we do there is roofing projects, window repair and replacement and masonry repair and replacement," said co-principal John Mecum. "It was a natural outgrowth of our preservation work. Firm members with specific training in that are now going after projects on their own."

"During the downturn we actually expanded that service," firm President Craig Lau noted with a hint of pride.

The industry "has changed a lot over the past 50 years," he reflected. "We have had to become more nimble and more strategic in the way we run our business."

Don Jacobson is a freelance writer in St. Paul and former ­editor of the Minnesota Real Estate Journal. He has covered Twin Cities commercial real estate for about 10 years.