The USS Zumwalt can hit targets from 100 miles away, provided the Navy can afford the cost of the projectiles.

Robert F. Bukaty / The Associated Press

PORTLAND, Maine — The new guns on the Navy’s biggest and most advanced destroyer are going to be firing blanks if the Navy can’t find cost-effective projectiles.

The GPS-guided, rocket-powered projectiles developed for the new 155mm Advanced Gun System currently cost about $800,000 apiece, nearly as much as a cruise missile, making them too expensive for the Navy to buy in large quantities, according to officials.

The projectiles were supposed to be less expensive than missiles, providing a cost-effective way to pummel targets from 70 miles away.

But the current price compares with $1 million for a cruise missile, which has a range of 1,000 miles. And the price is expected to grow, officials said.

For now, there are no plans to buy projectiles beyond the initial purchase of 90, according to the Navy’s draft 2018 budget.

It’s stunning news for a program plagued by growing costs.

“Congress is going to want to know how the Navy could get so far down the road without realizing that the price tag on these projectiles is so high,” said Loren Thompson, defense analyst at the Lexington Institute in Arlington, Virginia.

The Navy is evaluating alternatives for ammunition for the USS Zumwalt and two other ships in the class that are under construction at Bath Iron Works in Maine. Those options include both conventional and hyper-velocity projectiles, said Navy Capt. Thurraya Kent.

Bethesda, Maryland-based Lockheed Martin, which developed the 155mm projectiles, blamed the low production rate of ships — only three are being built, compared with the 32 originally envisioned — for driving up costs of the guided munitions.