Jim Michaels

USA TODAY

Donald Trump complained Sunday that the Obama administration announces in advance when and where it will attack the Islamic State, giving the enemy an advantage it shouldn’t have.

“We have announcements coming out of Washington and coming out of Iraq, we will be attacking Mosul in three weeks or four weeks,” the Republican candidate said at the presidential debate. “Why can’t they do the attack, make it a sneak attack, and after the attack is made, inform the American public that we’ve knocked out the leaders, we’ve had a tremendous success,” he asked.

It’s true that the element of surprise is an important principle in warfare, something that military strategist Sun Tzu pointed out more than 2,000 years ago.“Attack him where he is unprepared, appear where you are not expected,” Sun Tzu wrote in the Art of War, which is considered a bible for military strategists.

“We don’t do anything that is a surprise,” said Sebastian Gorka, a national security professor at the Institute of World Politics, who agrees with Trump's criticism. “We announce everything, down to the smallest detail.”

Recently, the White House announced the deployment of an additional 615 troops to Iraq to support the Mosul offensive.

Has the administration ignored the important principle of surprise?

Not really. Surprise can take many forms on the battlefield.

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Take Mosul, Iraq’s second-largest city: Trump is right that the Pentagon has signaled that the northern city is the next major battle in the fight to push militants out of Iraq. They've made that clear for months.

Publicizing an offensive, while withholding critical details, can serve a purpose. Civilians have time to prepare, fighters within the city might turn against Islamic State rulers and even allowing some extremists to flee might save the city from destruction.

"There could be a good military reason for it," said Michael O'Hanlon, an analyst at Brookings Institution.

O'Hanlon, however, said Trump's comments have triggered an important debate. "We've been a little too transparent and a little too vocal" in talking about the timing of the Mosul offensive, for example.

Still, it's nearly impossible to achieve the kind of surprise the Japanese pulled off at Pearl Harbor in 1941 when planning for a major ground offensive like Mosul.

The United States and its allies have been battling the Islamic State, which is also called ISIS or ISIL, for the past couple years and predicting the next step in the battle is not difficult. Iraqi security forces have already recaptured Ramadi, Fallujah, Tikrit and most other Iraqi cities that the Islamic State occupied. Mosul is the only large Iraqi city left.

The Islamic State views Mosul as its most important stronghold in Iraq. "You can't sneak up to someone’s capital city," said Michael Knights, an analyst at the Washington Institute for Near East Policy, a think tank in Washington, D.C.

A sneak attack would be hard to pull off. The militants have noticed the noose tightening around the city. The offensive will last months and involve thousands of troops, who are assembling in combat formations outside the city to cut off supply lines. There’s no way to keep that buildup secret.

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Iraqi forces have been taking villages and towns, including an air base it will use as a logistics hub for the eventual ground offensive. U.S.-led coalition aircraft have been attacking targets to pave the way for a ground offensive.

Without that large build up in forces, ousting the militants from Mosul would be a major risk. Several thousand fighters are inside the city and they have rigged the area with improvised explosives and other obstacles.

Keeping the buildup of forces secret in an age of social media and easily accessible satellite imagery is difficult, Knights said.

Iraqi forces can still maintain some surprise by keeping the precise time of the final assault secret and where they might breach militant defenses. Since the Iraqis are choosing the time of the attack, the United States has little control over those kinds of details.

The Germans, for example, knew the allies would invade Europe during World War II but an elaborate and successful deception plan kept them guessing as to where they would land.

"There's a difference between strategic surprise and tactical surprise," Knights said.

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Iraq’s armed forces have had a mixed record of changing their tactics to keep the enemy guessing. The offensive last year in Ramadi, a strategic Sunni city in western Iraq, took months and allowed many militants to filter out of the city.

The more recent offensive this year in Fallujah went quicker than militants anticipated, catching many by surprise. Islamic State forces rushed to escape in massive convoys that were attacked by waves of coalition aircraft. Hundreds of militants were killed in the coalition airstrikes.

It's easier to achieve surprise when launching individual airstrikes at key Islamic State leaders in Iraq and Syria. "Every airstrike we do is an example of superb tactical surprise," Knights said.