NORFOLK, Va. - Republican presidential nominee Mitt Romney tapped Rep. Paul Ryan as his running mate, rejecting more moderate and established choices in favor of a "young gun" of the conservative movement who has authored a fiscal roadmap of tough reforms to eliminate the nation's massive deficit, simplify the tax code and overhaul Medicare.

Romney made the announcement in front of the USS Wisconsin, the World War II-era battleship named for Ryan's home state.

Romney called Ryan "an intellectual leader of the Republican party," who "understands the fiscal challenges facing America, our exploding deficit and crushing debt, and the catastrophe that awaits us if we don't change course."

At 42, Ryan is among younger members serving in Congress, and is well below the average age of predecessors who have taken a spot on a presidential ticket.

But on Saturday he promoted his record as a mover and shaker in Congress. Ryan is serving his seventh term and is chairman of the powerful House Budget Committee, a position that has allowed him to take a leadership role in crafting the party's fiscal policies.

"I believe my record of getting things done in Congress will be a very helpful complement to Governor Romney’s executive and private sector success outside Washington," Ryan told an excited  crowd aboard the ship "I have worked closely with Republicans as well as Democrats to advance an agenda of economic growth, fiscal discipline, and job creation."

Ryan has a long tenure on Capitol Hill, first serving as a congressional aide before winning a seat in Congress in 1998. His fiscal aptitude and leadership skills have helped him rocket to the top of the GOP ranks, where he has won the respect of both the GOP leadership establishment and the new Tea Party faction.

Ryan on Saturday promised that the Romney-Ryan ticket "won't duck tough issues," a statement that hints at the coming entitlement reform pledges that will likely become part of the Romney-Ryan campaign platform.

"We can turn this thing around," Ryan said, touting a ticket with "the real courage to tell the truth."

Romney picked Ryan over former Minnesota Gov. TIm Pawlenty, Sen. Rob Portman, and Virginia Gov. Bob McDonnell.

Polling shows that while Ryan has low disapproval ratings, he is virtually unknown by the vast majority of voters.

In the coming weeks, both parties will be striving to define Ryan and his choice has already stirred Democratic disapproval.

As soon as Romney announced Ryan's name, Obama's campaign team sent out a blast email calling Ryan "the architect of the radical Republican House budget," that cuts taxes for the wealthy on the backs of the middle class.

Ryan's budget plan promises to lower the cost of Medicare by changing it to a "premium support system" and gradually raising the age of eligibility.

The Obama campaign wasted no time Saturday morning reviving a popular Democratic criticism of the Ryan budget, saying it would "end Medicare as we know it."

Ryan's plan would also reduce Medicaid costs by transforming it into a block grant system for states, a move he said would diminish incentive to increase its rolls.

"The downsides are obvious," University of Virginia political science professor Larry Sabato told The Washington Examiner. "Ryan's views on entitlements could widen the gender gap--women are very supportive of the safety net--and seniors are also skeptical. Those over 60 have been very supportive of Romney--to this point."

But in choosing Ryan, Romney  gave himself a much-needed boost among conservatives, especially those who have been irked with their presumptive nominee in recent weeks after a series of campaign gaffes. The most recent occurred last week when his campaign spokesman touted the health insurance mandate authored by the former Massachusetts governor, a plan that is much despised by the right and nearly cost him the nomination.

While Romney has always pledged to repeal the Affordable Health Care Act known as Obamacare, the addition of Ryan to the ticket will give the promise additional credibility, as  gutting the law is a principal element of the Ryan budget plan.

Conservative activists praised Romney's pick.

“Selecting someone like Paul Ryan, who is so popular with tea party activists, proves that Mitt Romney is committed to addressing the economic issues that have been troubling our nation for the last four years,” said Amy Kremer, chair of the Tea Party Express.

Romney's announcement comes at a time when his poll numbers have been sagging. Several national and swing state voter surveys show Romney trailing Obama by up to 9 points.

Political observers say it is unclear how whether Ryan will push those numbers up, particularly among critical Independent voters. .

"Ryan is an exciting pick that will fire up Republicans, and it indicates that Romney intends to present a compelling alternative vision for where he wants to take the country," said pollster Whit Ayres, who recently worked on Jon Huntsman's campaign.

Conservatives who turned out to hear the announcement praised Romney's choice.

"He has the right world values," Shirley Herline, of Norfolk, said as Ryan address the crowd. "And I just think he'll add excitement to the campaign."