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. They are always seen together, so it can be assumed that they live together in the house. Both 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 his 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 8am and 6pm, causing earthquakes for the Banks family.
Role in the films
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 he is going. When he responds, Admiral Boom orders Mr. Binnacle to enter it into the log. He then warns Bert of "heavy weather brewing there". He takes note of it, and thanks him. Admiral Boom is later seen firing his cannon at exactly 6pm. A few minutes after, George Banks passes by on his way home from work, and Admiral Boom inquires him about the state of the financial world. Admiral Boom then attempts to warn him of the environment at home, though his warning goes ignored.
The next morning, they are seen in the ship, watching a group of nanny applicants 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 8am.
The next morning, Admiral Boom takes note of the glorious day, and orders Mr. Binnacle to use a double charge of powder, to which he 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, Admiral 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 George has passed by a bit late than usual and calls out to him. However, he, being in a bad mood, goes by without even noticing Admiral Boom, who asks him 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, Jane, and Michael. Admiral Boom interprets the scene as an attack by "hottentots", and orders Mr. Binnacle to make preparations, which 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, they compliment him on his hit before ducking. The next morning, they take note of the wind shift, which has changed from east to west.
Mary Poppins Returns
Admiral Boom and Mr. Binnacle reappear in the sequel, this time having minor roles. Now since they are more elder, and take a bit longer to fire the cannon to mark the hour.
Admiral Boom and Mr. Binnacle are first seen at the beginning of the film where Admiral Boom tells his shipmate, telling him that William Weatherall Wilkins and the lawyers, Hamilton Gooding and Templeton Frye, "rung Big Ben too soon". Admiral Boom then warns Mr. Binnacle that Gooding and Frye have arrived. Just as they talk to the Banks family about the documents they need by Friday at midnight, Admiral Boom and Mr. Binnacle fire the cannon to mark the hour inside the house. Jane explains to Gooding and Frye that Admiral Boom fires the cannon for that reason. During the musical number "Can You Imagine That?", a sea captain and a shipmate identical to Admiral Boom and Mr. Binnacle briefly appear where Mary, John, Annabel, and Georgie explore the ocean in the magical world. The next day, Admiral Boom and Mr. Binnacle stare down at Jane who strolls by Cherry Tree Lane. When Mary, Jack, John, Annabel, and Georgie plan to go to Topsy's shop so she can fix the Royal Doulton bowl, Admiral Boom and Mr. Binnacle fire the cannon to mark the signal so they can get there.
Furthermore, they offer the Banks family, who are about to lose their home, to take up residence with them just as they fire the cannon while Big Ben begins to strike midnight and Jack prepares to stop it from doing so. 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 portrays him also portrays the bank chairman.