Why do retired IA Generals keep saying capture of DBO would fatally weaken India's control over Siachen Glacier?
One of the optical illusions of geography is that we think of Siachen Glacier as being at the source of the Nubra River, and we think of Karakoram Pass as that huge triangle away from it, somewhere to the northeast. How can losing KKP and DBO cause loss of Siachen? Or vice versa? Will PLA launch a blitzkrieg over the hitherto unpassable Saser La and thence to Nubra Valley?
Here's what can happen.
anupmisra had provided a very useful link to US Army maps a while ago. Study this plate carefully KKP and areas to its north and west
A couple of squares to the northwest of KKP is Yarkhand River. 4 squares to the west of KKP is Shaksgam Pass, and to the NW of Shaksgam Pass is Shaksgam RIver. Travel westwards along the Shaksgam River valley, you will see "camping grounds", and also several glaciers feeding S-N into the river. One of the is Urdok Glacier. Now follow Urdok Glacier to its saddle, and you arrive at... Indira Col.
Harish Kapadia is one of India's most highly regarded mountaineers right now, and he was given permission by IA to mount an expedition - he went up the Shyok River valley, to Gapshan, then to Teram Shehar Glacier (which he describes as a flat plateau), and thence to Siachen Glacier. While near Gapshan, he describes the view over Shaksgam Pass. Shaksgam Pass is one of the lesser known passes on the Silk Route, and it offers a gentle access right to Yarkhand River.
All of this is stuff for you to study in google 3D, now that I have oriented you to the strategic landmarks in the area.
What does this mean? It means that the Chinese have easy, almost motorable access right up to the northern access points to Siachen Glacier. If they try to do anything funny, IA will slaughter them because it controls Shaksgam Pass, which gives easy oversight of Yarkhand River headwaters and Shaksgam Valley. IA of course also guards Teram Shehar plateau, which is the easiest access to the entire glacier. But if India loses control over DBO, then a huge gateway to Siachen Glacier gets opened, and Indian positions on Siachen will be extremely vulnerable to not just a Chinese attack, but to a joint attack by China and the Pakis. That's why DBO protects Siachen, and vice versa.