Delta Air Lines, advancing its strategy of channeling capital into its existing fleet as opposed to more new aircraft, will pour $770 million into refreshing cabins and adding both seats and passenger creature comforts on 225 narrowbodies during the next three years.

The changes will see an array of improvements, including new slim-line seats with plug-in power, in-seat video, satellite TV, and revamped galleys and lavatories installed on 56 Boeing 757-200s, 43 737-800s, 57 Airbus A319, and 69 A320s.

The upgrades will add six economy seats to the A319s, boosting per-aircraft capacity to 102 seats. The A320s will get four additional first class seats and six more economy seats, pushing capacity to 126, which matches the carrier’s 737-800s.

The upgraded 757s include 49 for domestic services with 200 seats each: 20 in first class, 29 in Economy Comfort (EC), and 151 in economy. Seven more 757s will be configured for international routes with 197 seats in an 18-28-151 layout, which adds 23 seats to the carrier’s current international 757 cabin.

The airline operates 138 757s, including eight separate seating configurations. It was not immediately clear which of the domestic 757s were part of the upgrade plans.

Airbus aircraft upgrades including new first and business class seats, power at every seat, new galleys, and larger overhead bins.

New 757 amenities include in-seat video, satellite TV and access to power for every passenger, new galleys, updated LED cabin lighting, new lavatories and larger capacity overhead bins.

The 737-800s will receive new in-seat video, cabin lighting, and lavatories.

“We’re continuing to make smart long-term investments in our products and services to meet the expectations of our customers,” says Delta Executive VP and Chief Revenue Officer Glen Hauenstein. Once these and previously announced upgrades are done, Delta will have revamped the interiors of its entire mainline fleet in a six-year period, he notes.

Delta declined to comment on the suppliers for the new cabin work, but RBC Capital Markets analyst Robert Stallard reports that B/E Aerospace will supply its Pinnacle line of seating as well as lighting, galleys and other cabin upgrades. The in-flight entertainment supplier is Panasonic, Stallard says.

The investments and capacity bumps fit into Delta’s strategy of growing while minimizing overhead. Delta has put its 2014 capacity growth forecast at about 2% while operating 10 fewer aircraft (Aviation Daily, Dec. 13). A combination of upgauging—both by replacing smaller aircraft with larger ones and adding seats to existing airframes—will make the numbers work, Delta executives say.

The introduction of the first of 88 ex-Southwest Boeing 717s late last year is part of the process, as they are bumping some 50-seat regional jets from Delta’s schedule.

The investments also underscore Delta’s commitment to get the most out of its existing assets by investing to keep older planes reliable—via strategies like liberal spares provisioning, including in some cases buying entire aircraft for parts—as well as appealing to passengers.

“[W]hen you get on an airplane, if it’s well-maintained, it’s clean and it has a new interior on it, you really don’t know how old it is,” Hauenstein said last month at the airline’s annual investor day. “[A]re customers really willing to pay you for that [airframe] newness? I haven’t seen it.”

RBC’s Stallard points to Delta’s move as a potential harbinger among U.S. carriers.

“[T]he bigger picture positive is that we think this is a concrete sign of a pick up in airline retrofit spending,” Stallard notes. “With capacity expansion plans in place and global airlines in the black we think those with more dated fleets, such as the U.S. mainlines, will be investing in their cabin product in order to better compete, particularly in the higher margin business class product.”