Goofs

The planes on the sail appear and disappear in different shots.

When the submarine puts to sea soon after Monk and Natalie are on board, the Captain calls for a depth of 250 feet long before they have the chance to even clear port.

When Albright is at Natalie's house and talking to Monk, he puts his right hand down in front of him (he grabs his left hand, which has been down the whole time holding his cap). In the next shot, his right hand is by his side, way too quickly for him to have moved it there.

When Natalie and Albright kiss, the position of Natalie's left hand changes repeatedly.

After Lt. Albright asks Monk to go with him, Natalie helps Monk to put on his jacket, right arm first. In the next shot, Monk's putting on his right arm on the jacket again.

There are two problems with Monk and Natalie being trapped inside the ballast tank: First, the ballast tanks are not accessible from the inside of a submarine. The other problem is that the ballast tanks are only used to take the sub above or below the surface. Once below the surface, the ballast tanks are full. To dive or ascend, the submarine moves devices called "dive planes" up or down.

Commander Whitaker refers to his submarine as a "ship." In the US Navy, a submarine is a "boat."

The Commanding Officer would not be referred to by his rank (Commander) on board his ship. He would be called "Captain."

US submarines do not have a designated Medical Officer as part of the crew. They have an Independent Duty Corpsman, who is enlisted. Submarine Medical Officers are usually at shore commands and have a different warfare pin than regular submarine officers.

Jason Pierce is referred to as "Lieutenant Commander," but his shoulder bars have only two stripes, indicating that he is a Lieutenant.

While in the ballast tank, Monk tells Natalie that he doesn't know how to swim. Yet, when Stottlemeyer helped Monk fake his death at the end of Mr. Monk Is on the Run: Part 1 (2008), Monk fell into the ocean when Stottlemeyer "shot" him and he presumably swam to shore.

He did swim to shore. It took him a long time. And, when he came ashore, he indicated that it was a miracle that he survived.

Some of the items that appear on the walls of the Lieutenant's quarters also appear on the walls of the Captain's quarters, including a clock that always displays 6:22.

The Commanding Officer tells the Chief of the Boat to "Helm steer zero-five-zero." COB repeats the order as "zero-nine-zero."

The Commanding Officer mistakenly gives depth-change orders to the Chief of the Boat, rather than to the Officer of the Deck. Additionally, while depths of "one five zero" and "two five zero" feet are ordered correctly, the Captain orders "three zero zero" feet rather than the correct "three hundred" feet.

Lt. Steven (Casper Van Dien) says that the USS Seattle is a "Class 4 submarine." However, there is no such class. All submarine classes have names like "Seawolf," "Ohio," "Vanguard," and so on.

About halfway through, Steve, a military man, hands Monk, a former police detective, a gun, saying it's empty. Neither he, Monk, nor Natalie (also present) checks it or asks that it be checked.

As Monk and Natalie are debating whether or not to board the submarine, Monk mispronounces the word asphyxiation, dropping the "S" sound. He clearly says "aphyxiation".