In the older versions of Docker for Windows, I remember it explicitly said it used a linux VM for the kernel.
But since the new stable version (released in July 2016 I think), it says
Docker for Windows is a native Windows application with a native user interface and auto-update capability, deeply integrated with Windows native virtualization, Hyper-V, networking and file system
If I understand correctly, the specified base image is for the user space and the host's kernel is used. So, if I specify that I'm using an ubuntu base image to run the echo command, how does the Windows kernel come into play?