Underwater archaeology is considered as a branch of maritime archaeology (the archaeology of aquatic vessels and associated infrastructure), though not exclusively: underwater excavation techniques and methodology can also be applied in the study of sunken settlement and committal sites, for instance. underwater or maritime archaeology does not essentially deal with wrecks, even if that is the part scuba divers more often deal with.
Maritime archaeology has two important advantages over land archaeology. First the remains of ships and cargoes, even organic materials, are sometimes better preserved under water or in bottom sediments. The second advantage lies in the fact that until recently, shipwrecks were usually beyond the reach of human intervention or salvage, thereby creating perfect time capsules.