| 1. U |  | 76. under way |
| 2. U-boat | | 77. under weigh |
| 3. U-shaped frame | | 78. under-deck |
| 4. U.H.F., UHF | | 79. under-keel allowance |
| 5. U.K. | | 80. underbid |
| 6. U.K.H.A.D. | | 81. undercamassed |
| 7. U.L.C.C | | 82. undercarrier |
| 8. U.T. | | 83. undercharge |
| 9. u/i | | 84. undercoat |
| 10. UAM | | 85. undercoating |
| 11. UJSNH | | 86. underdeck cargo |
| 12. UK f.o. | | 87. underfoot |
| 13. UK/Cont. | | 88. underhand |
| 14. ukleja | | 89. underhaul |
| 15. układ podstawowy | | 90. underhung rudder |
| 16. ukośnica (Uk) | | 91. underinch |
| 17. ULCC | | 92. underkeel clearance |
| 18. ULD | | 93. underloading |
| 19. ulkhead deck | | 94. undermanned |
| 20. ullage | | 95. underpowered |
| 21. ullage board | | 96. underquote |
| 22. ullage foot | | 97. underrun |
| 23. ullage hole | | 98. underrun (a rope) |
| 24. ullage plug | | 99. underrun a net |
| 25. ullage report | | 100. underrun a tackle |
| 26. ullaged | | 101. underrunning |
| 27. Ulloa's circle | | 102. undersail |
| 28. ULMS | | 103. underset |
| 29. Ultimate Consignee | | 104. undersized fish |
| 30. ultimate stability | | 105. understaffed |
| 31. ultra large crude oil carrier | | 106. undertaking |
| 32. ultra quick flashing | | 107. undertone |
| 33. ultra-high frequency | | 108. undertone index |
| 34. ultrasonic test | | 109. undertow |
| 35. ultrasonic wave | | 110. underwater |
| 36. umbra | | 111. underwater body |
| 37. UMS | | 112. underwater burst |
| 38. una rig | | 113. underwater camera |
| 39. una-rigged boardboat | | 114. underwater concrete |
| 40. unattended light | | 115. underwater cutting |
| 41. unbalanced laminate | | 116. underwater cutting torch |
| 42. unbalanced rudder | | 117. underwater cutting torch lighter |
| 43. unbalanced weave | | 118. underwater explosion |
| 44. unbalanced woven rovings | | 119. underwater hull |
| 45. unballast | | 120. underwater lamp |
| 46. unbend | | 121. underwater range |
| 47. unberthed passenger | | 122. underwater tools |
| 48. unberthed ship | | 123. underwater torpedo tube |
| 49. unbitt | | 124. underwater valve |
| 50. uncapsizing ship | | 125. underwater vehicle |
| 51. uncharted | | 126. underwater welding |
| 52. UNCLOS | | 127. underwater-to-air missile |
| 53. uncoil | | 128. underwater-to-surface missile |
| 54. uncouple motions | | 129. underwater-torch |
| 55. uncovered | | 130. underway replenishment tanker |
| 56. undamped motion | | 131. underwrite |
| 57. undecked | | 132. underwriter |
| 58. under (strict) supervision | | 133. underwriting |
| 59. under bare poles | | 134. undisturbed flow |
| 60. under bevel | | 135. undo a nut |
| 61. under canvas | | 136. undock |
| 62. under construction | | 137. undulate |
| 63. under current | | 138. undulation |
| 64. under deck tonnage | | 139. undulatory |
| 65. under easy sail | | 140. unequal-angle bar |
| 66. under full sail | | 141. unfair holes |
| 67. under hatches | | 142. unfavourable winds |
| 68. under load | | 143. unfurl |
| 69. under repair | | 144. unhook |
| 70. under sail | | 145. unicellular foam (plastic) |
| 71. under sailing orders | | 146. unidentifiable cargo |
| 72. under ship's tockle | | 147. unidirectional (reinforced) composite |
| 73. under stress of weather | | 148. unidirectional cloth |
| 74. under the lee | | 149. uniform general cargo |
| 75. under the wind | | 150. uniform pitch |
