The importance of deep ocean observation has been gradually recognized to understand oceanic effects on the anthropogenic climate change accurately. A deep float is one of the most suitable devices to gather lots of oceanic profiles from deep ocean and a monitoring network with many deep floats, “deep Argo”, is strongly required to be built up even from social viewpoints. However, there are no floats available below 2,000 m depth and some institutes and float makers are now developing a deep float. In April 2013, Japan Agency for Marine-Earth Science and Technology and Tsurumi-Seiki Co. Ltd. succeeded development of a deep float, “Deep NINJA,” which can observe the deep ocean up to 4,000 m depth globally except for the throughout-a-year ice covered seas. Deep NINJA can operate most patterns of observation requested by users and the patterns are changeable even after deployment by sending e-mail commands. The float with lithium batteries is estimated to measure 45~51 CTD profiles from 4,000 dbar depth in its lifetime, which means that 2-year operation can be realized with 15-day observation interval. To enhance the data quality of the float observations, especially for salinity, it is strongly recommended that a shipboard observation be carried out at its deployment. The article, which is the latter part of the detail explanation on Deep NINJA technologies, will concentrate on those related to the functions for observation directly, e.g., sensor, depth control system, and lifetime (energy consumption). It will also describe the present status of the Southern Ocean observations by its small fleet shortly. And finally, we will mention current plans of its improvements and future prospects for its developments in observational ocean science.