## 1 Introduction  
On 6 January 2018, the Iranian oil tanker 'Sanchi' carrying 111,300 tons of condensate collided with the Hong Kong cargo ship 'Changfeng Crystal' in the East China sea, at approximately 160 nautical miles east of Shanghai. After the collision, the 'Sanchi' burned violently and exploded on 14 January. The 'Sanchi' sank 4 h after the explosion. Three people died and 29 people were missing in the accident, and oil leaked from the 'Sanchi' polluted 10 km\({}^{2}\) of sea area. After the accident, the State Oceanic Administration of China, the Maritime Search and Rescue Center of China, and the Maritime Search and Rescue Center of Shanghai launched the emergency response mission for the accident. Figure 1 is the scene of the accident.  
In this accident, the 'Sanchi' oil tanker carried a total of 113,000 tons of condensate. Condensate is a highly toxic and volatile chemical substance, and there is a risk of deflagration at any time after it leaks. Therefore, it is too dangerous for humans to enter the core area of the accident to perform a mission. We urgently needed a mobile unmanned platform to replace humans in the core area of the accident to obtain the necessary information, such as the submarine topography, the state of the shipwreck, the location of oil spills, and the situation of water pollution.  
Unmanned surface vehicles (USVs) are the suitable platform for an emergency response mission. Unmanned meant it could be deployed for a longer time, therefore widening the operational window. Most importantly, the use of the USVs resolved the security challenge of surveying in dangerous areas. In recent years, USVs have been widely researched and applied in a lot of fields [1]. Some new USVs are constantly developed, such as 'Spartan Scout' designed by the USV team in San Diego [2], 'Nighthawk' from AAC (Accurate Automation Corp) [3], and a range of USVs from ASV(The Company of Autonomous Surface Vechile), such as the USVs that called 'C-WORKER' and 'C-TARGET' [4]. Although USVs have many applications at this stage, they are limited to carrying out missions for scientific research, such as environmental monitoring [5; 6; 7], environmental sampling [8; 9], communication platform [10; 11], and harbor protection and patrol [12; 13; 14; 15]. However, emergency response mission for disaster or accident are performed by AUV(Autonomous Underwater Vehicle) or ROV(Remote Operated Vehicle), for example, [PERSON], [PERSON] et al. developed an AUV-based approach inspired by an existing small, long-range system, called the Tethys Long-Range AUV (LRAUV), in order to support the Arctic Doman Awareness Center (ADAC) for spill preparedness [16]. [PERSON], [PERSON] et al. used remote-controlled vehicles to quantify large animals at five study sites to determine the effects of the spill on deep-water animals [17].The only application of USVs for disaster was responding to Hurricane Wilma. During the rescue mission, the Center for Robot-Assisted Search and Rescue at the University of South Florida used a USV that called 'AEOS-1' to inspect docks and seawalls then bridges [18].  
In this emergency response mission, we deployed a newly designed USV. Compared with the previous USVs, (1) the improved navigation control algorithms (path following and collision avoidance) can provide high navigation accuracy while ensuring the navigation safety; (2) the improved LARS (Launch And Recovery System) enabled the USV to be quickly deployed and recovered in the mission area; and (3) a new pump sampling system, which is small in size and light in weight, can be installed or removed at any time.  
The rest of this paper is organized according to the structure below. In Section 2, we introduce the system architecture of the USV. The approach is proposed in Section 3. In Section 4, we introduce the mission process and analyze the mission data. Finally, the conclusion is given in Section 5.  
Figure 1: Accident scene.