Macro required to paste rows onto a single row until value changes in a column: HELP!!

Hello all,

Sorry about the ambiguous description but I'm not exactly sure how to best describe it. Best to look at the example attached.

I have a data dump with 400K rows. I need a macro to go down column B, and whilst the Acc_ID is the same, I need to paste the values in column B,C and D onto the same row as the first occurrence of the value in column B. Basically, I want to transpose the data into the first available blank column as long as my Acc_ID column has not changed. Once it changes, then that will be the next row that has values get copied on to as the macro goes down each row.

i would really appreciate any help at all. I'm ny good at writing macros at all and because the data is 400k rows long, I would really love to have a macro to do it for me.

Thanks in advance!