|This article is about the engine. You may be looking for the Story Library book.|
Rosie is a lively little tank engine who idolises Thomas, which sometimes bothers him. She works as both a shunting engine and a mixed traffic engine. She used to work mainly at the Knapford Shunting Yards, but is now based at Vicarstown.
Rosie began idolising Thomas to the point of hero-worship and imitation. Though this is said to be the most sincere form of flattery, it only served to irritate Thomas whilst he was trying to deliver a special birthday post train to Alice at High Farm. He even started to try and avoid her, but after Thomas had an accident in the course of delivering this train, Rosie helped him and he started to respect her.
Rosie was later called to help Thomas shunt trucks until Hector frightened her away.
Rosie was charged with acting as a back-engine to Emily with the funfair special. Wanting to take the train herself and thinking she was doing Emily a favour, Rosie succeeded only in creating confusion and delay on a grand scale, but eventually set things right.
Rosie rescued Thomas when his fire went out after playing a game of "Splish, Splash, Splosh". She later let Diesel take her train of flowers which was headed for market.
One day Rosie had a cracked wheel, so Thomas and Butch brought her a new one.
On Sodor Surprise Day, Thomas bumped some coal trucks to surprise Gordon, but ended up surprising her instead. She was later cleaned up with Whiff at the washdown and joined Gordon and Thomas at Callan Castle to see Harold decked out in bright lights to make Gordon laugh.
Sometime after she was repainted into her red livery, James challenged her to a race. When Rosie realised that there was something wrong with James' brakes, she warned him to go to the Steamworks to have them checked before they got worse. James did not follow her advice and as a result, when he sped down Gordon's Hill, his brakes would not work and he went on a runaway until he crashed into the wall at the end of Tidmouth Sheds.
Soon after, James went to the Vicarstown Goods Yard, looking for Henry's train to take to the Mainland. Rosie told him that she knew they were important and that was why Thomas came to take them earlier.
During Valentine's Day, Diesel bumped her just as Cranky was loading her flatbed with a crate of roses, which ended up crashing on the tracks. Bill and Ben later saw Thomas telling off Diesel, causing the twins to think they were attracted to each other, much to their embarrassment. A bit of teasing and a meet-up with Thomas at the washdown caused her to avoid him for fear of humiliation and she was not exactly pleased to know that she was heading to the same place he was. After a brief conversation with Edward, she rushed off so fast that she took the shunter's pole with her before it was moved out of the way. Thomas and Rosie ended up front to front at Vicarstown, where they made up for recent events and found that their specials were for Lady Hatt's Valentine's Day surprise.
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, and is very eager to prove her worth, as evidenced by her wanting to help Thomas deliver Alice's birthday presents, or even attempting to pull a special train on her own.
From Series 21 onwards, Rosie appears to have become more levelheaded and mature, serving as a voice of reason to James' arrogance. She also stands no nonsense for teasing or rudeness, although she does have a good sense of humour and likes a friendly joke.
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, who modified them for use 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 in the UK, including one at the Bluebell Railway and several more exist in various conditions throughout the world. In addition, several Yugoslavian-built copies of the S100 design also exist, including two that have been imported into the UK and modified to represent USA Class members.
From her debut up until The Great Race, Rosie was painted lavender with light grey tank panels, red lining and gold boiler bands. Her wheels were red with light grey wheel rims.
Starting from the twenty-first series onwards, Rosie is painted cherry red with dark raspberry tank panels, gold boiler bands and light grey lining. She has gold lining above her wheels and around her ladder. Rosie has the letters "NWR" written on her tank panels in light grey and the number "37" in light grey under her cab windows. She still retains her original red buffer beams and wheels with light grey wheel rims however.
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- 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.
- 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.
- Most merchandise lines depicted Rosie without the lip gloss and blush that she had worn prior to the twenty-first series.
- Since her debut, Rosie has appeared in every series and special except The Adventure Begins, which was set before she arrived on the railway and the twentieth series, possibly due to her model being reworked for the twenty-first series and Journey Beyond Sodor.
- Due to loads of fanmail asking for more Rosie, she was overhauled taking four months. The production team decided to completely rebuild her from scratch. 
- In the twenty-first series, Rosie was given the number 37, this is a reference to her being the thirty-seventh standard gauge engine to be introduced in the television series.
- According to SiF, Rosie was intended to have at least one other episode in the twenty-first series. This episode, along with seven others, were cancelled to make way for production of the twenty-second series.
- According to another tweet from SiF, other liveries considered for Rosie when she was updated for the twenty-first series, including blue and green. However, these were eventually rejected in favour of the red livery. 
- 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 recolour, most merchandise ranges give Rosie cherry red wheels, although her wheels still retain their original red colour.
- “Hello, I'm Rosie. I want to/wanna be just like Thomas, a really useful engine.”
- ―Rosie's website audio
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- Take Along (discontinued normal, metallic and "lights and sounds")
- Take-n-Play (normal, talking and glow racers; discontinued)
- Collectible Railway
- Motor Road and Rail (normal; discontinued, cherry red livery)
- TrackMaster (many versions all discontinued)
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- Mega Bloks (discontinued)
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- Boss (discontinued)
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- Adventures (normal and light-up racers; discontinued)
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