Egypt unrest: Military at heart of Egyptian state
In the six decades since 1952, when the Egyptian military brought an end to a century-and-a-half of monarchical rule, it has stood at the core of the Egyptian nation.
In this largely self-appointed position, the military underpinned a repressive police state and lost successive wars against Israel in 1948, 1956 and 1967 - the last in humiliating fashion.
Despite this, the institution has seamlessly woven itself not just into Egypt's structures of power but also its economy, society, and even imagination.
Its first advantage was to be present at the creation.
In 1952, a coalition of junior officers led by Gamal Abdel Nasser overthrew King Farouk, perceived as a corrupt British puppet.
Like many post-colonial armies in weak states, it immediately began to spin a narrative of modernity and heroism that, to a large degree, endures today.
The debates that have sprung up about the Muslim Brotherhood are echoes of those that took place in the 1950s, a period in which the army, at the high point of its clutch on the state, portrayed itself as the sole bulwark against Islamic extremism and the linchpin of regional stability, an image it still works to project today.
These efforts were greatly burnished by the famous surprise attack across the Suez Canal in 1973.
Despite Israel's subsequent advance to within 100km (62 miles) of Cairo and Egypt's post-war concession to stay out of most of the Sinai Peninsula, the strategy washed away much of the shame of the 1967 Six-Day War.
Throughout, the army has succeeded in preserving its reputation by cannily shifting the burden of repression onto the despised interior ministry and brutal secret police, or Mukhabarat. It is therefore in the regime, but not of it.
All of Egypt's post-1952 leaders have been military officers, and both serving and retired generals are sprinkled throughout the various arms of government.
In spite of this ubiquity, the army has cultivated the impression of standing above the fray, and therefore outside of the petty corruption and failures of governance that blight Egypt.
This has been all the easier because its grip extends well beyond the institutions of the state and into the economy.
Like the politically powerful armies of Turkey and Pakistan, the military receives lucrative sinecures and controls factories that produce everything from weapons to home appliances.
Barring an interlude between 1955-73, when Egypt tilted toward the Soviet Union, the US has stood closely alongside the institution. When the Camp David Accords led to the 1979 Israel-Egypt Peace Treaty, the American aid began flowing.
Since that crucial year - one in which the Middle East convulsed with the Iranian Revolution and the Soviet invasion of Afghanistan - annual US aid to Egypt has averaged $2bn. In 1980, it made up a tenth of Egypt's entire output.
This far exceeds even the large sums granted to Pakistan since 9/11, and has made Egypt the second-largest recipient of US aid behind Israel for most of this period.
The US long employed a 3:2 ratio in determining how much aid would go to Israel and Egypt respectively. Even though this has slipped over time, the Obama administration still sent $1.6bn in 2010. It planned to ask Congress for the same amount for 2011.
Has this aid been directed to alleviating poverty, or shoring up democratic forces?
Not quite. The military portion of assistance since 1987 has been $1.3bn annually.
Over the past decade-and-a-half, the proportion of non-military to military aid has fallen almost continuously. It may be at its most skewed for a generation, with US military aid to Egypt five times as large as all other aid.
US assistance has been estimated to account for up to 40-50% of Egypt's military spending, though the figure was closer to 25% in 2008, the latest available figures. But its contribution is greater than that in qualitative terms, given the benefits Egypt receives.
America has trained legions of Egyptian officers at its military schools, and sold Egypt advanced weapons platforms ranging from Apache helicopters to F-16 fighter jets.
These give it a regional fighting power matched only by Israel. Some of these sales, like those of the M1A1 Abrams tanks that have recently been deployed in Tahrir Square, entailed major technology transfers.
Given this huge US contribution to the Egyptian military, many had assumed that US pressure should be enough to encourage the generals to peel themselves away from Hosni Mubarak and lever him but of the presidential palace.
But this is premature. Knowing that the regime could endure for nine months, with or without Mr Mubarak himself, the military may be loath to abandon those who might yet wield the power to dismantle some of their privileges.
Moreover, the highest levels of military leadership have been tightly woven into the regime, as with the appointment of Omar Suleiman and Ahmed Shafiq, both intimately connected to the top generals.
But with so many of their resources flowing from Washington, loyalties may be split.
Junior officers may feel less beholden to the regime's patronage, but they are also less susceptible to American influence, making their decision-making highly unpredictable.
In any case, Egypt's low-ranking officers have been known since 1948 for lacking initiative.
It is US pressure on the senior echelons that will prove the most important determinant of events in the days and weeks that follow. This would be an ironic turn for an army claiming such intensely nationalist credentials.
Shashank Joshi is a doctoral student of international relations at the Department of Government, Harvard University, and Research Associate at the Royal United Services Institute.