The Navy plans to base 18 P-8A Poseidon jets at Kane'ohe Bay as replacements for the venerable P-3C Orion turboprop, a move that would result in fewer airplanes and personnel at the Marine Corps base, slightly more noise, and an investment of $169 million for infrastructure upgrades.

The Navy said in a draft environmental impact statement that it wants to begin replacing the aging Orions in its fleet no later than 2012 and have the process completed by 2019.

Under the "preferred" basing plan released Friday, 84 Poseidons would replace 120 of the older Orions at these bases: Kane'ohe Bay; Jacksonville, Fla.; and Whidbey Island, Wash. There also would be periodic squadron detachment to North Island, Calif.

Originally designed for hunting Soviet submarines, the P-3 Orion has been the Navy's frontline maritime patrol plane since the 1960s. The most capable Orion version is the P-3C, first delivered to the Navy in 1969.

After the 9/11 attacks, the Orion, with its long range, was pressed into overland service in Afghanistan, and Patrol Squad-ron 9, or VP-9, out of Kane'ohe Bay, conducted imaging, long-range targeting and firing of Stand-Off Land Attack missiles against Taliban and al-Qaida targets.

The Hawai'i-based Patrol Squadron 47 now is in Tallil, Iraq, with more than 350 sailors, using sophisticated surveillance sensors on missions in support of ground troops.

The Poseidon is a military version of the Boeing 737 commercial jet. Kane'ohe Bay would receive three squadrons with six of the planes in each squadron.

The Navy said the Poseidon is its "next generation" maritime patrol aircraft, and it has increased mission capabilities.

"The (P-8A) offers advantages over the P-3C in that it would increase mission reliability while requiring a smaller force and less maintenance infrastructure," the environmental report said.

Nearly a quarter of the Navy's fleet of 161 P-3 Orions were grounded in December due to fatigue in wing sections. The service said some of those planes were based at Kane'ohe Bay.

The Navy considered six alternatives in the environmental analysis for the new P-8A Poseidon, including a "no-action" alternative.

The report looked at having a permanent squadron detachment of Poseidons at Kane'ohe Bay, and two to three squadrons of six planes each, before deciding on the "preferred" alternative of three squadrons here.

Hickam Air Force Base was considered but eliminated as a potential home base because ordnance handling and storage next to Honolulu International Airport would not meet Defense Department safety criteria, and because there is not enough land and infrastructure to support the new planes.

Both the old and new planes can be armed with torpedoes, cruise missiles, bombs and mines.

The Navy will hold public hearings on the replacement aircraft plan and take public comment before reaching a final decision on basing. The Hawai'i hearing will be on April 1 at Castle High School, but Navy documents did not say at what hour. For more information, go to www.mmaeis.com/default.aspx.

The environmental report said the proposed action would mean replacing the older Orions with the new Poseidons at existing maritime patrol bases and allowing the use of existing infrastructure where possible.

The P-3C Orions operated from Barbers Point Naval Air Station before being shifted to Kane'ohe Bay.

According to the Navy report, each of the P-3C squadrons here has 346 personnel and nine primary aircraft. Under the replacement plan, each of the three squadrons at Kane'ohe Bay would have six planes and 166 personnel.

With additional support personnel, the total needed for the P-3Cs here is 1,641, according to the Navy. The environmental report predicts there will be 737 fewer personnel needed at Kane'ohe Bay with the replacement planes.

For the Hawai'i basing, $169 million in new construction would be required for upgrades including a new hangar, expanded parking apron and demolition of some existing infrastructure, including metal-frame warehouses.

While the two planes have different noise characteristics, the actual increase in noise would range from 1 to 2 decibels for the P-8A Poseidon, the Navy said.

"People at or in the immediate vicinity of (the Marine Corps base) would be exposed to slightly higher single-event noise levels during (P-8A) landings compared with current landing operations completed by P-3C aircraft," the report said.

Marine Corps Base Hawaii's workforce at Kane'ohe Bay includes 6,072 Marines, 2,765 sailors, and 2,340 civilians and contractors.

Reach William Cole at wcole@honoluluadvertiser.com.