This report looks at the responsibilities of states and companies involved in the transfer of military equipment by sea under customary international law. The maritime transport is by far the main modality for the transfers of military equipment and commodities. The report considers cases of irresponsible shipments of arms and military commodities to countries with ongoing armed conflicts and escalating human rights violations at the time when the transfers took place. Those shipments would have fallen under the prohibitions established by one or more articles of the Arms Trade Treaty, which came into force on 24 December 2014. All the concerned shipments were in effect at substantial risk of those arms and commodities being used to commit or facilitate serious violations of international human rights and humanitarian law. Military fuel and chemicals (such as white phosphorous) are not regulated by the ATT and the report wants to highlight their role in warfare with the aim to indicate a field for future improvements of the ATT. Effective regulation of the global trade in conventional arms and military commodities must further include adequate provisions to control their physical movement across international borders. Without such requirements, the ATT will fail to address a significant gap in international military equipment transfer controls, and will deprive the international community of a key tool to prevent arms transfers from being used to commit and facilitate serious violations of human rights. Chapter 1 highlights the role maritime transport plays in the world arms trade and its logistics. Chapter 2 analyses the legal and policy requirements for enhancing transparency and accountability in the transfer of arms and military commodities by sea. Chapter 3 focuses on container vessels as the backbone of the regular arms flows between exporting and importing countries. Chapter 4 illustrates the role of ships specialized in carrying dangerous cargoes and, in particular, ammunition. Chapter 5 focuses on the “arms ferries”, vehicles carriers called roll on/roll off that are able to transports thousands of military vehicles on wheel or tracks. Chapter 6 reports on cases of oil tankers that provided hundred of thousand tons of jet and diesel to a country involved in an armed conflict and severe human rights violations. Chapter 7 focuses on campaigns to stop irresponsible arms shipments. The report concludes by making a series of recommendations aimed at promoting compliance with the ATT and customary international law. These include the integration of transport arrangements for ATT- controlled goods into the risk assessment procedures for arms transfers; the publication of documentation related to the shipment of arms.