Newcastle faced a relegation battle in 1937–38, and Smith was transferred to Walter Crickmer's Manchester United for a club record £6,500 in February 1938. He scored on his debut in a win over Barnsley at Oakwell on 2 February, and totalled eight goals in 1937–38, as United finished in second place and were thus promoted back into the top-flight. The Red Devils then consolidated their First Division status with a 14th-place finish in 1938–39, Smith scoring six goals. The outbreak of World War II then meant that the Football League was suspended for seven whole seasons. Smith was prolific in the War League Western Division in 1939–40, scoring 16 goals in United's 22 matches. He stayed at Old Trafford in 1940–41, bagging 26 goals in the War League North Regional League, including five against Blackburn Rovers on 28 December. In 1941–42 he hit 18 goals, as United finished fourth in the first edition of the War League North Regional League, before winning the second instalment of the competition. Smith hit 36 goals in 1942–43, hitting hat-tricks against Blackburn Rovers, Manchester City, Wrexham (home and away), Everton, and Crewe Alexandra. He stayed on for the 1943–44 season, and hit 35 goals, bagging hat-tricks against Stockport County, Oldham Athletic, and Burnley; United finished second behind Blackpool in the first instalment of the regional league. He scored nine goals in 1944–45, and hit a hat-trick past Burnley in front of newly appointed manager Matt Busby. Smith struck 17 times in 1945–46, including once against Accrington Stanley at Peel Park in first edition of the FA Cup since the outbreak of war. He did not, however, score a goal during the 1946–47 campaign, as Busby led his team to a second-place finish in the First Division, one point behind Liverpool. Officially, Smith is recognised as having scored 15 league and cup goals for United during his career, but he also scored over 150 goals during the war. These goals are not counted towards the official total as they are classified as friendlies. During the war he also guested for Burnley and Blackburn Rovers. He left Manchester United after 15 goals in 41 league and cup games, and joined Eddie Hapgood's Blackburn Rovers for a £3,000 fee in March 1946. He was signed by Gordon Hodgson's Port Vale for a four-figure fee in May 1947. He scored on the penultimate day of the 1946–47 season,