Sobu-Yokosuka line (=横須賀総武線) means the operation route of one of the Rapid train network in Greater Tokyo. This train is operated on Sobu line, Tokaido line and Yokosuka line. Most of trains are operated between Chiba (=千葉) and Kurihama (=久里浜)/Yokosuka (=横須賀) via Tokyo (=東京) and Yokohama (=横浜). Some trains are extended to operate to Narita airport (=成田空港) and other stations in Chiba Pref. This train is a sort of commute train. But all trains have two double decker Green cars in the formation. Especially Rapid train to Narita airport may be replacement of Narita Express if you want to save the fare. These trains are fully covered by Japan Rail Pass. Of course if you use Japan Rail Pass Green, you can take Green cars with no extra cost.
Please refer the post of Rapid service network in Greater Tokyo. You can see some images of Green car and intrerior.
Route, schedule and trip time
This train is operated every 10 to 15 minutes between Chiba and Kurihama. And some trains are extended to operate to these following stations.
Narita airport — One or more trains every hour. 19 round trips a day.
Kimitsu (=君津) on Uchibo line — Mostly one train every hour. 15 round trips a day.
Kazusa-Ichinomiya (=上総一ノ宮) on Sotobo line — One train every hour to two hours. 9 round trips.
Naruto (=成東) on Sobu line — One round trip a day.
The train to Narita airport is called “Rapid Airport Narita” (=快速エアポート成田).
The trains stop at these following stations on basic route:
The trains to Narita airport stop at these following stations between Chiba and Narita airport:
Chiba-Tusga-Yokkaido-Monoi-Sakura-Shisui-Narita-Kukodainibiru (=Narita airport terminal 2)-Narita airport (=Narita airport terminal 1)
The trains to Kazusa-Ichinomiya stop at these following stations between Chiba and Kazusa-Ichinomiya:
The trains to Kimitsu stop at these following stations between Chiba and Kimitsu:
The trains to Narito stop at same stations between Chiba and Narita as train to Narita airport, then stop at all stations after Narita.
The travel time among the major stations are as follows:
Narita airport (Terminal 1)-(3min)-Kukodainibiru (Terminal 2)-(8min)-Narita-(13min)-Sakura-(17min)-Chiba
If you go to Yokohama, the Tokaido Shinkansen is not a good choice. It takes 19 minutes to Shin-Yokohama from Tokyo. It seems to be the fastest choice. But Shin-Yokohama is a few stations away from Yokohama. You have to take a local train to get Yokohama. You spend at least 20 minutes to transfer the trains at Shin-Yokohama and the travel time by the local train to Yokohama. This Rapid train is faster than the Shinkansen. This train takes you to Yokohama directly from Tokyo in 25 minutes. This is the fastest to get Yokohama.
If you go to Kamakura, This Yokosuka-Sobu Rapid train is most convenient. You can get Kamakura directly from Tokyo and Shinagawa.
At last, I would like to tell you one more thing. Tokyo station is a huge terminal station. Most of trains that include Shinkansen, Tokaido line, Chuo line (to Shinjuku), Yamanote line (circle line in downtown Tokyo) depart from the ground level platform. But Tokyo station has some more platforms underground too. Yokosuka-Sobu line and Narita Express depart from this underground level. Please expect at least 15 minutes to transfer the train when you use the train from underground level.