The Republican front-runner stood on a battleship in Los Angeles on Tuesday evening and largely dispensed with the idea that he would offer a broad foreign policy vision. Instead, the businessman spoke for under 15 minutes aboard the USS Iowa, returning to his tough rhetoric on immigration as several hundred protestors chanted their disapproval nearby.

There was no mention of ISIS, the Islamic militant group Trump has in the past pledged to eradicate, and few policy solutions to the rise of China, the nation he says is responsible for America's trade problems. Trump did once again blast the Iran nuclear deal reached by President Barack Obama and world powers, and offered some more details on his pledge to tear apart the Department of Veterans Affairs and improve health care for former service members.

"We're going to create a whole new system. We're going to take the system apart. You're going to get the greatest service of any country because you deserve it," Trump said. "We have illegal immigrants that are treated better, by far, than our veterans."

The meat of Trump's foreign policy speech centered on what has been at the heart of his meteoric rise to the top of national polls: Illegal immigration. As soon as the event got underway, several hundred protesters were allowed into the parking lot about 200 feet from the ship, chanting, "Racist, go home" and "Donald Trump is a racist."

"The drugs pour in, and the money pours out. Not a good deal," Trump said, recalling his visit to the Texas-Mexico border. "So we're going to build a wall."

The Republican presidential front-runner -- standing in front of three massive guns protruding at 45-degree angles from the battelship -- donned his now-trademark "Make America Great Again" hat as he bellowed into the microphone. When his remarks concluded, Trump threw hat after hat into the crowd as patriotic tunes blared.

Trump's remarks came one day before he is expected to be on the defensive Wednesday at CNN's debate, especially on foreign policy issues likely to be at the forefront of the 11-candidate squabble. Several rival GOP candidates have said they plan to take aim at the real estate mogul and press him on policy specifics.

Trump has recently struggled with some basic foreign policy questions, most prominently in an interview with conservative radio host Hugh Hewitt -- who will be one of the questioners at the CNN debate at the Reagan Library. Trump was flustered early in the interview when he appeared not to know the name of General Qassem Soleimani, the head of Iran's elite Quds Forces who has played a critical role in Iraq and in the fight against ISIS.

But he did little on Tuesday to display new national security credentials, mostly repeating his promises to recruit the nation's smartest negotiators that would execute his foreign policy. The American people, he repeated, are "disgusted" and he could change that.

"In the end, I want you people to look around and look at each other, because this is going to be a special day," he said.

CNN's Sara Murray and Jeremy Diamond contributed to this report