M
- Magi (Classical peoples: Magi)
- GWR Standard Goods 0-6-0 (1856 - 1879)
- Magpie (Bird: Magpie)
- CCR 4-4-0T (1861 - 1872)
- SDR 4-4-0ST (1872 - 1889)
- Mammoth (Powerful animal: Mammoth)
- GWR Pyracmon class 0-6-0 (1848 - 1873)
- Mars (Roman mythology: Mars)
- GWR Mather, Dixon 2-2-2 (1840 - 1840)
- GWR Fire Fly class 2-2-2 (1841 - 1868)
- Mazeppa (Literature: Mazeppa)
- GWR Fire Fly class 2-2-2 (1841 - 1868)
- SDR Eagle class 4-4-0ST (1859 - 1885)
- Medea (Greek mythology: Medea)
- GWR Fire Fly class 2-2-2 (1842 - 1873)
- Medusa (Greek mythology: Medusa)
- GWR Fire Fly class 2-2-2 (1842 - 1864)
- Melling
- GWR Hawthorn class 2-4-0 (1865 - 1877)
- GWR Hawthorn class 2-4-0T (1877 - 1892)
- Mentor (Greek mythology: Mentor)
- GWR Fire Fly class 2-2-2 (1841 - 1867)
- Mercury (Roman mythology: Mercury)
- GWR Mather, Dixon 2-2-2 (1839 - 1843)
- GWR Fire Fly class 2-2-2 (1841 - 1865)
- Meridian
- GWR Sun class 2-2-2 (1840 - 1870)
- Mersey (Geography: River Mersey)
- GWR Standard Goods 0-6-0 (1857 - 1879)
- Meteor (Speed: Meteor)
- GWR Sun class 2-2-2 (1840 - 1864)
- SDR Comet class 4-4-0ST (1851 - 1881)
- Metis (Greek mythology: Metis)
- GWR Standard Goods 0-6-0 (1855 - 1877)
- Midas (Greek mythology: Midas)
- GWR Standard Goods 0-6-0 (1854 - 1875)
- Miles
- GWR Sir Watkin class 0-6-0T (1866 - 1888)
- Milo (Roman personality: Titus Annius Milo)
- GWR Fire Fly class 2-2-2 (1841 - 1866)
- Minerva (Roman mythology: Minerva)
- GWR Standard Goods 0-6-0 (1853 - 1877)
- Minos (Greek mythology: Minos)
- GWR Fire Fly class 2-2-2 (1841 - 1870)
- Mogul (Leader of people: Mogul)
- GWR Metropolitan class 2-4-0T (1862 - 1872)
- Mole (Geography: River Mole)
- NDR 2-2-2 (1855 - 1870)
- Monarch (Leader of people Monarch)
- GWR Standard Goods 0-6-0 (1853 - 1879)
- Moose (Animal: Moose)
- GWR Prince class 2-2-2 (1846 - 1870)
- Morning Star
- GWR Star class 2-2-2 (1839 - 1869)
- Mosquito (Insect: Mosquito)
- GWR Metropolitan class 2-4-0T (1862 - 1877)
- Murdoch (Famous engineer: William Murdoch)
- GWR Hawthorn class 2-4-0 (1865 - 1892)
- Myrtle (Flower: Myrtle)
- GWR Metropolitan class 2-4-0T (1864 - 1873)
Read more about this topic: List Of Broad Gauge (7 Feet) Railway Locomotive Names