तमन्ना जहाज के सफर की... क्यों करूं मैं, दिन भर की खुशियाँ लम्हों मे बर्बाद क्यों करूं मैं। - Amir

there is nothing specific that only Wap 5 or WAP 7 can haul Rajdhani..... there were times when BCT Raj was hauled by Wap 4 as well.
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Now regarding the availability if WAP 5 or WAP 7...the train will run on the loco that is free...since these trains are Rajdhani type ..hence they will be mostly allotted a 3 phaser loco....in any case the train is not going to go faster nor reach its destination early just because it gets a WAP 5 instead if WAP 7

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well he never suggested that P5 or P7 should haul these trains. And regarding locos P5's were once common with these two until they were taken off last april/may.

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Before WAP4's, GZB WAP1's used to haul BCT/AK Raj from BRC to NDLS/NZM.
And they used to get twin diesels (WDM2/2B/2C, I think) between BCT to BRC :D
WAP1 locos used to haul a majority of Rajdhanis in the past and used to maintain schedules easily :)

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those days existed before many of us were out of half-pants :D
Although it is interesting to see that time, as back then 12951 used to take 19 hrs, now it takes far less :)

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