Like a lot of networks as they move into original series, Tribune’s WGN America doesn’t yet seem to know what it wants to be when it grows up. So the channel is following the witchy (but not terribly bewitching) “Salem” with “Manhattan,” a dense ensemble drama devoted to the scientists involved in the Manhattan Project, which devised the first nuclear bombs. Opening, as the on-air script informs us, “766 days before Hiroshima,” the show establishes plenty of room to operate. But the program’s dense, grim nature augurs a rather narrow appeal, leaving a different sort of cloud hanging over its prospects.

Tellingly, the cast of “Manhattan” is listed in alphabetical order, suggesting a level of equality that’s both accurate and somewhat confining. Despite boasting some fine actors, without a central lead, the project tends to careen around like loose ions, lacking a stabilizing core.

The driving focus, naturally, is on the race to produce a weapon devastating enough to end WWII, which is what motivates Frank Winter (John Benjamin Hickey), who leads one of the competing teams, and never stops reminding his charges about the steady increase in combat casualties. His brilliance, however, is offset by the unproven nature of his work and his bull-in-a-china-shop demeanor — the lack of social graces and scientific genius being a not-unusual combination.

The introduction to all of this comes through Charlie (Ashley Zukerman), a new arrival who doesn’t know what he’s been enlisted to produce. Like the other scientists, he must lie to his spouse (Rachel Brosnahan), who quickly befriends Winter’s wife (Olivia Williams, especially good), as the families must survive in what amounts to ramshackle barracks in the Los Alamos desert.

While Charlie doesn’t wind up working for Winter, everyone is in the uncomfortable position of trying to impress Robert Oppenheimer (Daniel London), who, at least initially, is seen about as often as the President was supposed to be at first in “The West Wing” — an occasional presence spoken of in hushed, reverent tones.

Written by Sam Shaw and directed by Thomas Schlamme (yes, a “West Wing” alum), “Manhattan” earns points for being serious and ambitious, while creating a strong sense of atmosphere and place in the isolation — and paranoia — in which the families must exist. The promising cast includes Daniel Stern as Winter’s more politically astute colleague and Mark Moses as the facility’s military overseer.

Taking all those factors into account in decidedly unscientific fashion, “Manhattan” certainly isn’t a bomb creatively speaking, nor is it yet the bomb, in latter-day vernacular. And perhaps appropriately, as admirable as some of its elements are, what’s missing in the opening hours is the elusive spark necessary to make them genuinely pop.