As Bert's introduction states, Admiral Boom and Mr. Binnacle were once members of England's navy. Given Admiral Boom's mention of "hottentots", it's likely that some of their military service took place in South Africa, probably during the Boer Wars of the 1880s and 1890s.
As of 1910, they live a short distance from the Banks home, in a house with a ship on the roof. The two men are always seen together, so it can be assumed that they live together in the house. Both men seem to be friendly with the Banks family, though Admiral Boom is usually the one to speak to others. Admiral Boom has a larger role in the film, as he interacts with the Banks family, while Mr. Binnacle is usually seen following the Admiral's orders.
In the ship, Admiral Boom is the commander, with Mr. Binnacle as first mate. From the ship, they are capable of seeing much of the neighborhood, and thus often know what is going on around them. They also fire a cannon twice a day, at 8 AM and 6 PM, causing earthquakes for the Banks.
Admiral Boom and Mr. Binnacle are first seen as Bert is showing the viewers the way to 17 Cherry Tree Lane. As Bert is passing by the houses, he takes time to introduce Admiral Boom. He explains that Admiral Boom was in the navy, and thus keeps his home "shipshape." Admiral Boom sees Bert from the ship and asks where the man is going. When Bert responds, Admiral Boom orders Mr. Binnacle to enter it into the log. He then warns Bert, of "heavy weather brewing there". Bert takes note of the warning, and thanks him. Admiral Boom is later seen firing his cannon at exactly 6 PM. A few minutes after, Mr. Banks passes by on his way home from work, and the Admiral inquires him about the state of the financial world. The Admiral then attempts to warn him of the environment at home, though his warning goes ignored.
The next morning, the two men are seen in the ship, watching a group of nannies who have lined up at the Banks' home. Admiral Boom notes that the lot of them make a very ghastly looking crew. They later fire the Morning cannon at exactly 8 AM.
The next morning, Boom takes note of the glorious day, and orders Mr. Binnacle to use a double charge of powder, to which the first mate happily agrees. Later, Mr. Binnacle is seen washing windows in a lifeboat, with Admiral Boom observing when they see Mary Poppins on an outing with Jane and Michael Banks. After learning they are going to the fish market, Boom happily orders Michael to proceed at flank speed. He then asks Mr. Binnacle to put his back into his cleaning, noting that the world needs more hard work.
That night, after firing the Evening cannon, Admiral Boom notices that Mr. Banks has passed by a bit late than usual and calls out to him. However, Mr. Banks, being in a bad mood, goes by without even noticing the Admiral. Admiral Boom asks Mr. Banks if something is bothering him, but he is ignored once again.
The following evening, Admiral Boom and Mr. Binnacle are later shown watching as Bert and the chimney sweeps are dancing for Mary and the children. Admiral Boom interprets the scene as an attack by "hottentots", and orders Mr. Binnacle to make preparations. The preparations are revealed to be the firing of fireworks from their cannon. They watch as the entire group rushes for the chimney of the Banks' home. Admiral Boom then orders a second firing. When Bert uses his broom to return one of the fireworks, similarly to cricket, the two men compliment him on his hit before ducking. The next morning, the Admiral and Mr. Binnacle take note of the wind shift, which has changed from East to West.
Admiral Boom and Mr. Binnacle reappear in the sequel, Now since they are more elder, and take a bit longer to fire the cannon to mark the hour. Later in the film, they offer the Banks, who are about to lose their home in Number 17, to take up residence with them. They later appear at the end of the film at the carnival and fly with balloons.
- Admiral Boom appears as a minor character in the theatrical version of Mary Poppins. In some productions, the actor who plays his role also performs the role of the Bank Chairman.