The Philadelphia firm of KieranTimberlake has been chosen from a starry competition by the State Department to design the new U.S. Embassy in London. KieranTimberlake won the project over Thom Mayne’s firm, Morphosis; Richard Meier & Partners; and Pei Cobb Freed. You know it’s an important job because Meier’s firm has issued a news release saying that it didn’t win.

The selection helps to define the next chapters of a drawn-out transatlantic tale of diplomacy. The embassy’s move has been complicated by debates over the future of the Americans’ existing Eero Saarinen–designed facility (sold to Qatari developers last year). There has also been sniveling by British architectural arbiters over the new embassy site’s master plan, designed by Americans, of course (specifically, Zimmer Gunsul Frasca Architects), which was revealed last summer. Oddly, the name of Prince Charles has not yet come up in the conversation.

The $1 billion project* is probably not the tradition-loving prince’s type of building, though it’s far more inventive than most other embassies produced in recent years by the State Department’s Bureau of Overseas Buildings Operations, or OBO. The OBO has completed 50 new embassies and 69 new diplomatic facilities worldwide since 2001**; this is but the fourth embassy design competition since that which Saarinen won for London in 1956. In recent years, especially, the bureau seemed to have decided that good-looking buildings were anathema to security needs, which are indeed pressing: Since 1998, there have been more than 150 attacks on U.S. government properties overseas.

KieranTimberlake’s renderings suggest that any battlements will be cannily disguised. The new London embassy design will be a glass cube set atop concrete stilts, veiled on three sides in tented layers of lightweight polymer shades that hold solar panels and make the surface interesting. The embassy grounds, designed with the landscape architect Laurie Olin, will create the required 100-foot-deep security buffer from the street by placing the building inside eccentric circles of parklike spaces that terrace upward to the entrance.

The embassy is moving from its current location on Grosvenor Square in central London. Its new incarnation will occupy five acres in the southwest part of the city, near the Battersea Power Station, where a Rafael Viñoly–designed redevelopment scheme budgeted at 5.5 billion pounds was approved by the government this week. The embassy site lies on the south bank of the Thames River, a mile downstream from London’s heart.

Groundbreaking is scheduled for 2013, and the building is supposed to open in 2017.

*Correction, Feb. 25, 2010: The original version of this article stated that the new London embassy would cost $500 million. In fact, that is the construction budget.

**Correction, March 3, 2010: The original version of this article stated that the OBO had completed "about 40" embassies since 2001.