What is known about the Walker-Vanquisher collision

Why did HMS Walker and HMS Vanquisher collide in September 1939?

The available account points to close formation work at night in poor weather, but it does not establish a more precise cause.

Walker and Vanquisher were operating close together at night in poor weather. Those are the main circumstances available in the account. The damage photographs prompt a tentative impression that Vanquisher came onto Walker, rather than Walker onto Vanquisher. That interpretation remains uncertain and does not establish blame.