| | Uncle Poo | 1983 | Diatec | unclepoo | | 6.33 |
| | Under Defeat (GDL-0035) | 2005 | G-Rev | undefeat | | 0.00 |
 | Under Fire (Japan) (clone of: undrfire) | 1993 | Taito Corporation | undrfirej | | 0.00 |
| Under Fire (US) (clone of: undrfire) | 1993 | Taito America Corporation | undrfireu | | 0.00 |
| Under Fire (World) | 1993 | Taito Corporation Japan | undrfire | Shooter / Gun | 5.00 |
| | Under Siege (Maygay) (M1A/B) | 1969 | Maygay | m1undsie | | 0.00 |
 | Undercover Cops (Alpha Renewal Version) (clone of: uccops) | 1992 | Irem | uccopsar | | 0.00 |
| Undercover Cops (Japan) (clone of: uccops) | 1992 | Irem | uccopsj | Fighter / 2.5D | 0.00 |
| Undercover Cops (US) (clone of: uccops) | 1992 | Irem | uccopsu | | 0.00 |
| Undercover Cops (World) | 1992 | Irem | uccops | Fighter / 2.5D | 7.86 |
| | Unibox (Union) (MPU4, set 1) | 1969 | Union | m4unibox | | 0.00 |
| | Unibox (Union) (MPU4, set 2) (clone of: m4unibox) | 1969 | Union | m4uniboxa | | 0.00 |
| | Union Jackpot (JPM) (SYSTEM5, set 1) | 1969 | JPM | j5uj | | 0.00 |
| | Union Jackpot (JPM) (SYSTEM5, set 2) (clone of: j5uj) | 1969 | JPM | j5uja | | 0.00 |
| | Union Jackpot (JPM) (SYSTEM5, set 3) (clone of: j5uj) | 1969 | JPM | j5ujb | | 0.00 |
| | Unique (Union) (MPU4, set 1) | 1969 | Union | m4unique | | 0.00 |
| | Unique (Union) (MPU4, set 2) (clone of: m4unique) | 1969 | Union | m4uniquep | | 0.00 |
| | Universe (Barcrest) (Dutch) (MPU4) (DUN) | 1969 | Barcrest | m4univ | | 0.00 |
 | UniWar S | 1980 | Irem | uniwars | Shooter / Gallery | 6.75 |
| | unknown '008' (Unk) (MPS) | 1969 | | j2008 | | 0.00 |
