The United States has resumed taking delivery of the F-35 jets fitted with an interim upgrade following a halt that stretched to months over software delays and will withhold some payments until the remaining enhancements are done, senior officials quoted by Reuters said on Saturday.
The jets have gotten some much-needed upgrades through a Lockheed Martin programme, involving key suppliers, called Technology Refresh 3, or TR-3, which aims to improve the displays and the processing power.
"We are starting to accept deliveries of TR-3...It is a truncated version...and does not have all the functionality that we want, but it is far enough along that we can accept delivery now," Secretary of the Air Force Frank Kendall said.
TR-3 includes hardware and software improvements and is just one piece of a broader upgrade to the nation's stealth jet known as Block 4.
"The hardware of that seems to be coming along fine but the software is lagging," Kendall told reporters at the Royal International Air Tattoo in Britain.
"We are at a point now where we can accept aircraft with the understanding that additional increments of software have to go in to get it to where we need it to be."
Assistant Secretary of the Air Force for Acquisition, Technology, and Logistics Andrew Hunter stated that the decision to restart the deliveries prior to completion of the software upgrade was to keep other features from being delayed further.
"Waiting and waiting and waiting to finalise those capabilities that weren't quite ready is actually holding up progress on some of the later capabilities that we also really need," he said.
Hunter said the Pentagon will still withhold a portion of the final payments for each jet but declined to say how much.
So far, about $7 million of each jet's final payment has been held back. Each jet is worth about $100 million.
"Not everything we contracted for has been delivered... We will not pay for that which we have not received," Hunter said.
Offsetting the frustration of the delays, Hunter said the work to finish TR-3 has forged closer cooperation between companies involved in the world's largest defence program.
"We are going to work very hard to ensure that that process of bringing down those barriers continues so that Block 4 comes through when we need it," he said.