▁The ▁term ▁" o cean ▁l iner " ▁has ▁come ▁to ▁be ▁used ▁inter change ably ▁with ▁" pass enger ▁l iner ", ▁although ▁it ▁can ▁refer ▁to ▁a ▁cargo ▁l iner ▁or ▁cargo - pass enger ▁l iner . ▁ ▁Begin ning ▁at ▁the ▁advent ▁of ▁the ▁Jet ▁Age , ▁where ▁trans o cean ic ▁ship ▁service ▁decl ined , ▁a ▁grad ual ▁transition ▁from ▁passenger ▁ships ▁as ▁mean ▁of ▁transport ation ▁to ▁now ad ays ▁cru ise ▁ships ▁started . ▁In ▁order ▁for ▁ocean ▁lin ers ▁to ▁remain ▁prof itable , ▁cru ise ▁lines ▁have ▁modified ▁some ▁of ▁them ▁to ▁operate ▁on ▁cru ise ▁routes , ▁such ▁as ▁Queen ▁Elizabeth ▁ 2 ▁and ▁. ▁C ertain ▁characteristics ▁of ▁older ▁ocean ▁lin ers ▁made ▁them ▁un su itable ▁for ▁cru ising , ▁such ▁as ▁high ▁fuel ▁consumption , ▁deep ▁dra ug ht ▁prevent ing ▁them ▁from ▁entering ▁shall ow ▁ports , ▁and ▁cab ins ▁( o ften ▁window less ) ▁designed ▁to ▁maxim ize ▁passenger ▁numbers ▁rather ▁than ▁comfort . ▁The ▁Italian ▁Line ' s ▁ ▁and ▁, ▁the ▁last ▁ocean ▁lin ers ▁to ▁be ▁built ▁primarily ▁for ▁crossing ▁the ▁North ▁Atlantic , ▁could ▁not ▁be ▁converted ▁econom ically ▁and ▁had ▁short ▁care ers . ▁ ▁History ▁▁ 1 9 th ▁century ▁ ▁At ▁the ▁beginning ▁of ▁the ▁ 1 9 th ▁century , ▁the ▁Indust rial ▁Revolution ▁and ▁the ▁inter - cont inental ▁trade ▁rendered ▁the ▁development ▁of ▁secure ▁links ▁between ▁contin ents ▁imper ative . ▁Being ▁at ▁the ▁top ▁among