The start of the assault on the ISIS stronghold of Mosul, in northern Iraq, was heralded by a broadcast message from Iraqi Prime Minister Haider al-Abadi on October 16. He advised residents to hunker down. It was a message echoed by a massive leaflet campaign.

The US Republican presidential candidate, Donald Trump, has fiercely criticized the Obama administration for telegraphing the assault to the enemy. In the third presidential debate, he called it a stupid move that could cause the offensive to fail. He said World War II Generals George Patton and Douglas MacArthur would be turning in their graves. He says the attack has been public knowledge for months. He asked: Whatever happened to the element of surprise?

Surprise has always been an important instrument in a general’s toolbox. It’s the military equivalent of the sucker punch — catching the enemy with its guard down.

Military theorists talk about the effects of shock, significantly degrading an enemy’s combat effectiveness. Surprise can increase the attacker’s chances of success and can reduce casualties.

The obvious danger of telegraphing your objective is that the enemy can prepare. They can increase the depth and sophistication of their defenses: fortifying strongpoints; preparing fields of fire; laying mines and booby traps. They can concentrate their resources and combat power, and prepare reinforcements.

The enemy can also decide to retreat. Or enemey forces can use the time to prepare and mount counter-attacks to divert and distract the attacker’s main effort, as ISIS appears to be doing this week in Sinjar and Kirkuk.

So Trump’s criticisms appear worth investigating.

The first point to note is that this is not a US decision. The US is one partner among many in an Iraqi-led operation. There's a host of allies, with competing agendas — international powers like France, Turkey and Iran. Then there’s a host of competing Iraqi actors. Most notably, there are the Kurds and the official government army.

But there are also huge contributions being made by a variety of Shiite militias; a pro-Baathist militia; Sunni groups, and assorted Christian groups: Assyrians, Chaldeans. It would be a challenge, to say the least, to ask all these partners to keep a secret.

So did the Iraqis give the game away? At first glance, it would appear so, at least at the strategic level. However, there's a distinction to be made between strategic surprise and tactical surprise. That's the difference between the enemy knowing your ultimate objective, and them knowing how an attack will be made.

So it should be clear to any armchair general that strategic surprise is difficult where there's such an obvious objective. Also, you cannot easily hide massive physical preparations, especially in an open society, heavily infiltrated with sympathizers and spies. You need to mobilize your reserves, collect and train militia and paramilitary volunteers. You need to negotiate and bring in international support. Then there’s simple and highly visible activities, like stockpiling fuel, food and ammunition.

However, you can still achieve tactical surprise by coming at an unexpected hour, from an unexpected direction, with an unexpected force.

One of the most successful surprises in military history was perhaps the Allied invasion of German-occupied France during World War II: the D-Day landings in 1944. The Germans, strategically, knew an Allied invasion was coming but were surprised tactically: They were deceived into expecting an attack in the Pas-de-Calais region rather than on the Normandy beaches.

Similarly, the North Koreans were expecting a UN counter attack in the fall of 1950, but were totally surprised by MacArthur's invasion from the sea — his amphibious assault at Incheon, which totally transformed the course of the Korean War, freeing the south from Communist occupation.

On the other hand, surprise is no guarantee of success. The effects of shock can wear off quickly. Military theorists estimate an enemy can recover from shock in three days, sometimes less.

During Operation Market Garden in the fall of 1944, the Allies made a surprise set of airborne assaults to capture key bridges in Holland, to open the invasion route into Germany. But one bridge, at Arnhem, was simply too far for the land forces to reach. The Germans were able to recover from their surprise and destroy the British division there.

Likewise, Confederate General Robert E. Lee led a surprise invasion of Pennsylvania in the summer of 1863. But Union forces were able to recover and redeploy and ultimately confronted Lee successfully at Gettysburg.

Then there are good reasons why surprise might not be the best thing.

Commanders might decide that it’s more important, for moral or political reasons, to warn civilians, to minimize the risk of casualties among the innocent. That might increase the risk of battle casualties among your own forces in the short term. But such compassion might also shorten the war.

There might also be perfectly good short-term military reasons not to seek surprise.

First, there’s a psychological effect in conveying to the enemy that an overwhelming force is headed their way. That can be intimidating; causing desertion and wearing down the will to resist.

Second, if you invest the battle with prestige, you can make it politically difficult for the enemy to retreat without a major loss of face. Prestige and reputation are hugely significant in insurgent warfare.

Third, you can make an enemy bring in more resources, including perhaps vital reserves of men and supplies. If your goal is attrition, then that’s a good thing.

Finally, political needs might outweigh military imperatives — domestic or international politics.

It’s not yet public knowledge why the Iraqi authorities decided to telegraph the Mosul assault so publicly. We will have to wait until we see those documents currently marked top secret, or read the memoirs of key leaders, to be certain.

But as a student of military history, I would put forward a hypothesis, awaiting proof: Surprise was forfeited for political reasons. Not the political reasons that Donald Trump is putting forward, that the whole offensive is designed to help Hillary Clinton. It’s absurd to suggest that such a complex coalition of actors with such competing agendas could come together, at this moment in time, for such a parochial political motive.

Rather, I would argue that surprise was forfeited for Iraq’s internal political needs, to galvanize resources and support in what is a very fractured society. Every advance in Mosul is a political statement, and a political challenge, deciding which of the coalition forces is to occupy which village. A Kurdish movement into an Assyrian Christian village could cause problems; but a Shiite militia move into a Sunni village could provoke a new civil war. These movements are hugely controversial and are probably negotiated well in advance, to avoid antagonisms or even in-fighting.

This is not one single coherent, disciplined force. The most important key to success in Mosul is to keep that coalition together — much more important than maintaining the element of surprise.

So most likely, in my judgment, surprise was never even an option in Mosul. But we’ll need to wait for history to make the final verdict on that.

From PRI's The World ©2016 PRI