WASHINGTON (Reuters) - GenCorp Inc (>> Gencorp Inc) Chief Executive Officer Scott Seymour on Friday took over as head of the company's Aerojet Rocketdyne unit after the abrupt departure of its president, Warren Boley.

Boley's departure was effective immediately, said GenCorp spokesman Glenn Mahone. He said Seymour would remain chief executive and president of the parent company, which makes equipment for the aerospace and defense sector.

Seymour announced the news in a statement to employees on Friday, telling them he remained confident in the company's ability to deliver results for customers, shareholders and employees.

Sources familiar with the company said Boley and Seymour disagreed about the company's future.

"It was time for a change. There had been differences about the company's direction," said one source who was not authorized to speak publicly.

Boley declined comment on the reason for his departure, but said he was upbeat about the company's prospects. "Great company, great portfolio, great future," he told Reuters.

Boley said he was weighing future opportunities, including his role leading a family manufacturing business in Illinois that builds heavy equipment for the oil, gas and mining sectors.

Boley's sudden departure from Aerojet Rocketdyne comes at an uncertain time in the rocket-launch business and growing concern about the use of Russian-built rocket engines to power the rockets that lift U.S. satellites into space.

In October, GenCorp said it took a $17.5 million loss due to issues with the AJ-26 rocket engine that it provides for the Antares launch vehicle built by Orbital Sciences Corp, which this week completed its merger with Alliant Techsystems Inc, forming a new company known as Orbital ATK (>> ORBL ATK).

Orbital last year said it would swap out Aerojet's AJ-26 engine, which is based on the aging Soviet-era NK-22 engine, a move that came even before an Antares rocket exploded seconds after liftoff destroying a cargo ship bound for the International Space Station.

Last May, an AJ-26 engine exploded during a ground test at NASA's Stennis Space Center in Mississippi.

Aerojet Rocketdyne is also vying for a role in replacing the RD-180, a newer Russia-built engine that powers the Atlas 5 rocket used to lift U.S. military and spy satellites into space.

The Air Force is weighing how to reduce U.S. reliance on the RD-180 engines given rising tensions with Russia over its actions in Ukraine.

Boley first joined Aerojet as president in July 2012 and was named president of Aerojet Rocketdyne in June 2013 after the GenCorp acquired Pratt & Whitney Rocketdyne from United Technologies Corp (>> United Technologies Corporation).

Boley headed Pratt's military engine business for one year until May 2011, when he was replaced by Bennett Croswell.

Seymour, a longtime executive with Northrop Grumman Corp (>> Northrop Grumman Corporation), was named in 2010 to head GenCorp, and also headed the Aerojet unit from 2010 to 2012.

(Reporting by Andrea Shalal; Editing by Bernard Orr and Lisa Shumaker)

By Andrea Shalal