Rosie

Rosie is a lively little tank engine who idolises Thomas. She works as both a shunting engine and a mixed traffic engine.

Personality
Rosie is a friendly, respectful and helpful tank engine who likes Thomas very much. She and Thomas like to have fun, and also like to help each other when they are working. Rosie can be described as a feisty, energetic and free-spirited tomboy who is not afraid to do hard work. She loves to race just as much as she loves to be Really Useful.

Rosie also seems very eager to prove her worth, as evidenced by her wanting to help Thomas deliver Alice's birthday presents, or even pull a special train on her own. As of Season 21, she appears to have become more levelheaded and mature, serving as a voice of reason to James' arrogance.

Basis
Rosie is based on an SR USA Class 0-6-0T. Originally classified as the USATC S100 Class and designed for shunting duties in Europe during the Second World War, after the war ended, fifteen of these engines were sold to the Southern Railway where they were used as dockyard shunters at Southampton. There, they worked alongside the LB&SCR E2s (Thomas' class). Both classes were replaced by BR Class 07 diesels (Salty's class) in 1962, though members of the class remained in service on departmental duties until 1966.

Four members of this class are preserved, one at the Bluebell Railway. Two S100s have also been bought from the former Yugoslavia and modified to USA condition.

Trivia

 * Rosie is the first engine of several things:
 * The first engine of an American class introduced in the television series and the second such engine (after Stanley) introduced in the franchise overall.
 * The first engine in the television series to have their debut livery changed permanently and the second character in the television series overall, the first being S.C. Ruffey.
 * The first engine in the television series to receive a number who did not already have one.
 * The first engine in the television series to be lettered for the North Western Railway. She is the second in the franchise overall after Emma.
 * Rosie's model is currently on display at Drayton Manor. Sometime in 2017, a part of her siderod had broken off.
 * In Red for Rosie, one illustration incorrectly depicts her with a tender.
 * Most merchandise lines depicted Rosie without the lip gloss and blush that she had worn prior to the twenty-first season.
 * Rosie's whistle is a higher pitched version of Thomas'.
 * A magazine fact file states that she works on Thomas' Branch Line, although she is yet to be seen doing so in the television series.
 * The My First Thomas & Friends' Railway Pals variant of Rosie was the first piece of merchandise to introduce her in her new red livery.
 * Since her debut, Rosie has appeared in every season and special except The Adventure Begins, which was set before she arrived on the railway, and the twentieth season, possibly due to her model being reworked for the twenty-first season and Journey Beyond Sodor.
 * Rosie has both her whistle and connecting rods in different positions compared to her prototype:
 * Rosie's whistle is positioned behind her rear dome whilst her prototype has its whistle positioned on the right side of the middle dome.
 * Rosie's connecting rods are attached to her middle driving wheels whereas her prototype has its connecting rods attached to the rear driving wheels.
 * Her funnel is also taller than her basis.
 * Rosie has had a few modifications throughout the television series, which include:
 * Season 12:
 * Her tail-lamp was removed.
 * Season 13:
 * Her face became slightly smaller.
 * Her funnel and steam pipes became thinner.
 * Her lamp-irons were removed.
 * A detail on her coal bunker had been pushed in.