Do I need a proxy, tunnel or gateway?

I have three computers on my network: computer_1, computer_2, and computer_3.

Computer_3 can access computer_2

Computer_2 can access computer_1

I need to access Computer_1 from Computer_3.

Computer_2 has two network interfaces.

How can I do it?

I think to use a proxy or a http tunnel, but I have no idea how to enable communication between computer_1 and computer_3.

I need to access a web service running on Computer_3 from Computer_1.

All computers have Windows 7 64 bits.

Maybe I can do from Computer_3 this call: http://Computer_2/WebApi, and then Computer_2 redirects this call to http://Computer_1/WebApi.