By Adam Brookes
BBC News, Baghdad
A while ago, I stood on a porch in a small American town with the father of a fallen marine.
Many fewer US soldiers have been killed in Iraq in recent months
He described a sense of utter aloneness among the rituals that accompany a marine's death - the flag, funeral, memorial quilt. The naming of a high school gymnasium.
The US military is, perhaps understandably, unwilling to discuss publicly its true feelings regarding the deaths of 4,000 of its men and women. Senior officers say they do not hold with "milestones".
"No casualty is more or less significant than another; each soldier, marine, airman and sailor is equally precious and their loss equally tragic," said US military spokesman Rear Admiral Greg Smith.
The military tells us that more is to be learned by looking at trends - the way in which US soldiers have died, and with what frequency.
And the figures tell us that many fewer have been killed in recent months.
In April 2004, 135 US personnel were killed - half of them by "hostile fire", the remainder by IEDs (improvised explosive devices), car bombs, and other weapons. A few - nine - died in accidents.
In 2004, US troops fought a burgeoning insurgency in Iraq
The worst month was November that same year - 137 dead.
2004 was the year when the military was confronting a burgeoning insurgency and Shia militias in fierce combat.
For months, the numbers fluctuated: 49 here, 80 there, a steady stream of shattered American families.
Then, again, in late 2006 and into 2007, the numbers climbed.
In May 2007, 127 died. But by then many more were dying in bombings, rather than by hostile fire. And these numbers reflected the wave of sectarian violence, and the subsequent "troop surge".
But by early 2008, the numbers were sharply down. In January, there were 31 deaths.
Camp Victory is the largest US military base in Baghdad: an improvised, utilitarian fastness of trailers, concrete and vehicle parks, its soundtrack the roar of Blackhawk helicopters.
Amid this bleakness, Saddam Hussein's palaces surround a lake, massive and incongruous. The bathrooms still have cheap, ornate mirrors and gilt taps.
Here, I talked to Brigadier General Edward Cardon, who is the deputy commander of Multinational Force Central (MNF-C).
He breaks down "in no particular order" the reasons why the US casualty figures have dropped.
First, he says, experience. Officers and senior NCOs are frequently on their second or third tour in Iraq, and experience pays.
Second, the "troop surge". More combat units have pushed forward into Iraqi towns and stayed there, operating out of patrol bases rather than pulling back into larger fortified areas. Presence pays.
Third, the surprising degree to which Sunni Muslims have begun co-operating with the Iraqi government and armed forces and the US military. The "Awakening Councils" have organised 90,000 Sunni men - some of them former insurgents - into neighbourhood patrols and checkpoints.
These groups are paid by the US military out of commanders' discretionary funds, the general says. But the US does not supply them with weapons or ammunition - that they must do themselves.
And they must give biometric information about themselves - fingerprints and retinal scans - to the US military.
Fourth, the ceasefire announced by the largest Shia militia, the Mehdi Army, loyal to Moqtada Sadr.
And fifth, the increasing effectiveness of Iraq's armed forces.
"One year ago," says Gen Cardon, "my troops were experiencing an average of 25 attacks a day. Now, it's two a day, and sometimes none."
But he is quick to acknowledge the particular resilience of al-Qaeda in Iraq.
"These people have a remarkable ability to regenerate themselves. Time and time again they have shown a capability to pull off high-profile attacks," Gen Cardon says.
And Shia politicians in Iraq profess concern about the growth of the Awakening Councils. A Shia lawmaker told me she worried "what the Awakening groups would become in the future, whether they will be new Sunni militias".
'Nothing is predictable'
The drop in US casualties of late is echoed in lower casualty figures among civilians and among Iraqi troops.
But the causes underlying this diminution in death are complex and reversible. There is nothing here that serves as a predictor of how the casualty rates will look in a year's time.
After all, nothing in this conflict has been predictable.
I asked a colonel of the US infantry - a veteran of the invasion and two more tours in Iraq - whether, as his unit rolled into Baghdad back in 2003, he had imagined he would still be coming back in 2008.
"Never in my wildest dreams," he answered.