PORTLAND — Building a 292-mile pipeline is like choreographing a complex military operation: You must coordinate far-flung units, provide logistical support when and where needed, and pray for good weather.

When construction of the Portland Natural Gas Pipeline System kicked off in earnest June 8, five crews were on the job, working north from Plaistow, N.H., north from Wells, northeast from Albany Township, west from Gilead and southeast from Dummer, N.H.

Spokesman John Flumerfelt likens the process to a moving assembly line in which separate crews move into an area to clear the terrain, dig the trench, weld the pipe sections, lay the pipe and backfill and restore the site.

The project’s biggest technical challenge — the crossing of the Piscataqua River between Eliot and Newington, N.H., was completed in May, before full-fledged construction got under way.

By midsummer, when the process is at its height, as many as 100 crews will be at work between Haverhill, Mass., and Pittsburg, N.H.

On average, a crew can complete about a half-mile of pipe per day, as long as the supply line doesn’t hit a snag.

“When we have a trench open and we’re ready to put the pipe in, the pipe had better be there,” Flumerfelt said.

Bad weather can affect the construction timetable, as it did last month when a rainy spell gripped the state for more than a week.

“It was a killer. It was unbelievable how much water was out there,” Flumerfelt said.

The stakes are enormous. The cost of the line is roughly $1.2 million to $1.4 million per mile for the 30-inch section and slightly less for the 24-inch.

The pipe is made up of 100,000 tons of steel from mills in California and Alabama, at a cost of $70 million.

“The Titanic was 48,000 tons,” Flumerfelt said. “This is enough steel for two Titanics.”