Upheaval in Egypt has raised fresh questions about the role of US military aid in promoting American interests, as Washington struggles to distance itself from President Hosni Mubarak's autocratic rule.
For Egyptian protesters, F-16 fighters buzzing overhead and Abrams tanks rumbling through the streets symbolize Washington's long-running ties to the Egyptian regime, even as President Barack Obama presses Mubarak to relinquish power.
But for Washington, supplying weapons and training to Egypt and other countries is touted as a wise investment, extending American influence and safeguarding the peace treaty between Egypt and Israel.
US military aid to Cairo, amounting to $1.3 billion a year, represents one of the most prominent and costly examples of how Washington conducts diplomacy through its vast military and defense industry.
But the approach carries risks, as the aid does not ensure Washington's word will be followed while linking the United States to repressive regimes and human rights abuses, from Saudi Arabia to Uzbekistan.
"What you're dealing with is a balance, the assistance you provide gives you some -- but incomplete -- influence over what they do," said Stephen Biddle, a senior fellow at the Council on Foreign Relations.
"And the assistance implicates you to some degree but not completely in what they do," he said. "So there's an upside and there's a downside."
For more than three decades, US fighter jets, tanks and helicopters for Cairo have underpinned the country's peace deal with Washington's ally, Israel, while delivering access to Egyptian air bases and safe passage for American warships moving through the Suez Canal.
US officials believe years of American training programs for Egyptian officers may have even paid off in recent days and helped contribute to the army's refusal so far to open fire on demonstrators demanding Mubarak step down.
Admiral Mike Mullen, the chairman of the US Joint Chiefs of Staff, praised the Egyptian army this week for its "professionalism" after speaking by phone to his counterpart.
"Clearly it's a very volatile, uncertain situation but the chairman would very much like the relationship we have with the Egyptian military to continue," his spokesman, Captain John Kirby, told AFP.
Senator Lindsey Graham makes no apologies for Washington's support of Egypt's army, saying it serves as insurance to prevent Islamist hardliners from gaining power.
"Every American should be very appreciative of the fact that for years we've been providing aid to the Egyptian army in terms of equipment and training, because that army is our ace in the hole, as a world, to make sure Egypt doesn't go into a radical state," Graham said Tuesday.
Lawmakers, however, have voiced mounting frustration over the benefits of another military relationship -- in Pakistan -- where public hostility to US policies runs deep.
Despite billions in military aid and weapons, Pakistan's army has repeatedly put off cracking down on militants in North Waziristan that stage attacks on US-led troops in Afghanistan.
Mullen and others argue that cultivating military ties and providing hardware is vital as a way of defusing tensions and promoting long-term interests, even if it does not guarantee that US advice and demands will be met.
Defense Secretary Robert Gates has called the severing of military ties with Pakistan in the 1990s a strategic blunder that meant a generation of Pakistani officers had no contact with the US armed forces.
"When we've cut our mil-to-mil ties, it's really cost us," said Richard Fontaine, a senior fellow at the Center for New American Security.
Chaotic scenes on Cairo's streets have prompted comparisons to the 1979 revolution in Iran, where an out-of-touch regime had strong ties to the US military.
The Pentagon's investment in the former Shah's army and air force became a liability, with Iranians viewing Washington as propping up a corrupt monarchy.
When it comes to US military aid, Biddle said, Iran is an example of the "worst case scenario."